A quiet suburban mom, a hard-drinking war correspondent and an Arctic researcher were hiding in plain sight, championed by the Kremlin’s No. 1 fan of spy fiction

MI6 had a secret so sensitive that Slovenia’s spy chief needed to fly to London to hear it in person.

Somewhere in his tiny Alpine nation, a pair of elite Russian spies were hiding under deep cover. But the British intelligence agency couldn’t—or wouldn’t—tell him their names. The CIA had heard about them just days earlier.

Josko Kadivnik, director of Slovenia’s intelligence service Sova, meaning Owl, felt his stomach sink. In its three decades of independence, Slovenia had never arrested such a spy. Now, just weeks after Russia’s 2022 invasion of Ukraine, he was being tasked with a mission that went far beyond Slovenia’s borders to the heart of a New Cold War: His small team of officers needed to capture two Russian sleeper agents.

The stakes of this mission lay in Russia, where jail cells were filling up with political prisoners and a growing list of Americans seized as hostages in a geopolitical game of arresting and trading people like pawns. For every Russian spy the U.S. and its allies could capture, one of the Kremlin’s prisoners could be exchanged into freedom.

Working out of the Central Intelligence Agency’s headquarters, analysts in the mission center known as “Russia House” had been mapping a network of “illegals”: spies who spent years delicately weaving themselves into the fabric of Western society. They included Russian intelligence officers posing as Brazilian researchers in the Arctic and at Johns Hopkins University; and a Spanish news reporter working on Ukraine’s front lines.

The Kremlin called these foot soldiers Vladimir Putin’s “invisible front,” an army of agents living false lives on foreign passports and second languages. Identifying one, American spy catchers would complain, was like finding a needle hiding in a needle stack. Few would prove as well-concealed as Kadivnik’s target.

The story of how the West hunted those sleeper agents has never been told. Wall Street Journal reporters worked on three continents and spoke to more than 30 former and current officials in the countries where they operated: Slovenia, Argentina, Norway, Greece, Poland, Ukraine, the U.K., Canada and the U.S. Hundreds of court documents and personal records revealed painstakingly built false biographies, from a fraudulent Mexican passport to a doctored Greek birth certificate. The spies left behind a trail of confused friends, colleagues, and romantic partners, more than two dozen of whom spoke in detail about the people they thought they knew.

The clandestine transnational pursuit hinged on lucky breaks and leaps of faith. One country after the next would identify a spy only to face the same ethical quandary: Should the illegals be outed, to end their activities, or silently studied to unlock their networks and the riddle of why Putin invests so much in this mysterious tradition? Each day brought the risk that the prey could catch wind and flee. By the time the Greek National Intelligence Service went to investigate a Russian woman living undercover, she had already vanished, cleaning out her knitwear boutique in the shadow of the Acropolis, leaving a longtime boyfriend bereft and confused.

Kadivnik was determined not to let his targets, whoever they were, slip away. Tall with a shaved head, the intelligence chief had spent so long running operations against organized crime bosses that colleagues joked he’d adopted their flair for chunky silver neckchains and salty language. This next operation would have to proceed without a single leak in a country of just 2.1 million where a significant percentage still sympathized with Russia.

The spies he was after were much closer than he realized: a husband and wife living in a quiet suburban lane less than 3 miles from his office. The couple had spent more than a decade molding themselves into an Argentine family of four, all of them conversing in fluent Spanish. Not even their own children knew who they really were.

In 1968, a 15-year-old Vladimir Putin watched the biggest Soviet TV spectacle of the year: “The Shield and Sword.” The four-part miniseries heralded the fictional exploits of a Communist agent whose masterful command of German allowed him to pass as “Johann Weiss,” an SS officer delicately extracting the Third Reich’s deepest secrets.

The U.S.S.R. was stagnating behind the capitalist West, but its films, novels and even postage stamps were celebrating a human weapon Moscow possessed that Washington lacked: sleeper agents. In Soviet mythology, these heroes were the antithesis of James Bond, chameleons who could blend into the enemy’s nest, surviving not on martini-infused bravado and a license to kill, but on patience, wits and a monk-like capacity to sacrifice in service to the motherland.

Decades later, Putin would recall the effect the TV thriller had on him. He studied German in high school, then walked into his local KGB office and volunteered for a life undercover.

The young Putin had become entranced by a tradition whose origins stretched back to the 1917 Revolution, when the new Bolshevik government, unrecognized and encircled by hostile neighbors, couldn’t place spies under diplomatic cover in embassies abroad. Instead, its Communist agents acquired new passports. They honed second languages to operate as sleepers behind enemy lines. The spies had a unique strength (they could operate undetected) offset by a weakness (they had no diplomatic immunity and could thus be arrested for espionage).

Back in the U.S.S.R., their legend burned bright through stories of illegals like Rudolf Abel, who helped steal atomic secrets and was later depicted in Steven Spielberg’s “Bridge of Spies.” In reality, illegals often grew bored and depressed, burdened with long stretches between instructions and the constant stress of withholding a double life from the friends, lovers, spouses and children they accumulated abroad. Some simply walked away from their missions, joining the prosperity of the unsuspecting West, taking their secrets to their graves.

The KGB didn’t offer young Putin a chance to vanish into Europe as an illegal, though he would later claim to have managed several as an officer posted to 1980s Dresden. In his first-ever TV appearance, in 1991, he re-enacted the closing scene from a Soviet spy drama about an illegal in Berlin. That year, the Soviet Union collapsed and shortly after a fledgling democratic government broke the KGB into smaller, weakened agencies, leaving the West to assume the illegals program would expire.

In truth, the Soviet collapse left a network of sleeper agents stranded abroad, still living undercover, awaiting orders from a vanished empire. By the turn of the millennium, Putin was president, reinvigorating the program he’d idolized as a young man.

Under his watch, dedicated schools trained an army of new recruits in the languages, history and cultural habits of target countries. Young officers were encouraged to marry fellow agents, for cover and to ward off loneliness. Many studied Spanish and Portuguese to deploy to Latin America, where Russia could exploit patchy birth records and corrupt officials to more quickly secure a new identity. They could be activated at Putin’s direction.

In American suburbs, FBI agents were stalking the secret agents, watching from auditorium seats at their children’s school functions, or sneaking into their colonial-style homes in the dead of night to plant bugs and copy the floppy disks they used to communicate. By 2010, the FBI swooped in, announcing the arrest of 10 undercover spies. At least four had children, now left to wrestle with the revelation of their parents’ identity, and the question of where was home.

Another spy, Anna Chapman, had left behind a trail of former lovers and a confused ex-husband, a story condensed under headlines like “Russian spy babe’s hot affair.” Within two weeks of their arrest, all of the spies were swapped on a Vienna runway for four Russians Moscow had imprisoned for collaborating with the West, including Sergei Skripal, a military-intelligence officer who had given MI6 the names of Russian agents.

Putin’s most prized agents were reduced to tabloid fodder and later inspiration for a six-season FX series, “The Americans.” After their return, Putin joined the illegals in front of a live band for a rousing singalong of the theme song from “The Shield and Sword,” entitled “Where Does the Motherland Begin?”

The Obama administration sang a different tune. Eager to maintain its “reset” of relations with Moscow, senior officials played down the discovery of Russian spies living in suburbia as an anachronistic artifact of the Cold War.

It was anything but. Almost as soon as the swap was over, another generation of illegals was heading back into the field, their operations relayed in regular briefings to Russia’s most powerful fan of spy fiction.

Pablo González was a spy hiding in plain sight.

When protesters thronged the streets of Kyiv, braving gunfire to oust their pro-Russian government in 2014, the bearded freelance reporter was in the crowd, charming pro-Western activists with his booming baritone and a taste for danger. Early on, the photojournalists he teamed up with noticed he tended to bash out articles after several beers. Closing his laptop, he would talk animatedly about the Kremlin’s military strategy—or the women he’d conquered.

He explained his fluent Russian with shifting stories, at first telling a few friends he had studied it in college before explaining the full picture: He had spent part of his childhood in Russia, where his grandfather had fled after the Spanish Civil War.

Born Pavel Rubtsov in Moscow, he had left Russia with his mother for Spain’s Basque Country when he was 9. There, he took his mother’s maiden name, González. Spanish authorities would later suspect he had been recruited by the GRU, Russia’s military-intelligence agency, on a visit to see his father and stepmother around 2010.

González, who had fathered four children by a Spanish wife and Russian girlfriend, was an attractive potential asset. The bilingual and truly bicultural news reporter could use his freelance writing for Spanish media outlets as cover for operations. The GRU could offer him money and membership in a secret army to help them monitor two of their key targets, Ukraine’s westernizing army and Russia’s exiled opposition.

Within a year of Ukraine’s 2014 revolution, he had charmed and drunk his way into the company of the lawmakers, press secretaries and customs officials of the new Ukraine, cataloging his victories in text files he left on his laptop, under innocuous headings like “Business Trip to Ukraine.” His handlers would urge him to be more careful, to delete incriminating documents. He, in turn, would bill them for the tiniest expenses, down to the cheap bottles of wine he brought to meetings with Russians living in exile.

Meanwhile, officials at Ukraine’s Defense Ministry took a liking to the daring, garrulous war reporter, and regularly invited him to functions, including a 2016 tour of a base near the Polish border where he witnessed new NATO-structured military exercises and spoke with U.S. and Canadian instructors.

The next year, González on his own initiative tried to befriend Putin’s most feared opponent, opposition leader Alexei Navalny, who had traveled to Barcelona for eye treatment after unknown assailants attacked him with antiseptic green dye. González slipped into the clinic, offered Navalny help translating and navigating Barcelona, then took a selfie with him. He later sent his GRU handlers the address and descriptive details of the hospital, even the Wi-Fi passwords of a cafe where Navalny’s supporters were hanging out. Months later, he joined the protest leader for an evening of drinks with prominent Russian opposition figures, none of them wise to the GRU spy at their table.

González was working for the GRU’s 5th Department, one of two competing directorates Putin had expanded to seed sleeper agents abroad. The GRU encouraged its officers, nicknamed “Boots,” to take risks for quick results. For a Boot, the fluent Spanish-speaker was an unusual asset. Usually, the GRU trained and dispatched illegals so fast that their accents still betrayed a Slavic lilt. They sometimes tried to explain themselves with patchy back stories that fell apart under even light scrutiny.

The Boots’ rivals were the “Slippers” of Russia’s Foreign Intelligence Service, or SVR, who prided themselves on floating undetected. SVR operatives spent so many years acculturating themselves to the minute details of their supposed homelands—the way its citizens hold their cutlery, stand at a bar or smoke cigarettes—that the best could pass for natives of countries they only arrived in as adults. They were patient. And just as Pablo González began hopping around Ukraine, two of them, more tortoise-like, had arrived in Buenos Aires.

On June 14, 2013, a diminutive woman with mousy brown hair calling herself María Rosa Mayer Muños walked into the Italian hospital in Buenos Aires, with barely an hour left in her pregnancy, to face one of her most difficult endeavors as an undercover spy: birthing a child without betraying her true identity.

Obstetrician Mario Pérez had already logged in his notes that the woman had conspicuously little interaction with staff at the private hospital, one of the best in the Argentine capital. She had waited more than halfway through her term to book her first consultation. Now she walked into the basement delivery room fully dilated, he said. “She made us all run!”

Dr. Pérez had no idea that “Maria” was Anna Dultseva, on a yearslong journey to transform her life into the perfect lie.

Born in the Soviet city of Gorky, she married her husband Artem in 2004, then joined the SVR with him, she later told the spy service’s magazine. She spent three years in immersive training to transform herself into an alter-ego, built on documents seen by the Journal. First, she secured the Greek birth certificate of a dead child, doctored to claim the mother was Mexican. She used that to obtain a Mexican passport. Finally, she moved to Argentina in 2012 to join Artem, who was using the fraudulent papers of Ludwig Gisch, born in Namibia to an Argentine mother.

They lived in a building in the middle-class Buenos Aires neighborhood of Belgrano, attracting little attention among the 146 apartments and rarely attending tenants’ meetings. The concierge saw them come and go at routine times, with Artem usually wearing a tie.

By 2014 they had both secured Argentine citizenship and Anna was pregnant again. In the delivery room, medical staff had noticed she was calm—barely speaking, save for some quiet words for her husband in fluent Spanish. “This woman has a very high tolerance for pain,” Dr. Pérez said. The couple cooed over their new son, Daniel—a true Argentine citizen by birth, like his older sister, Sophie. No one came to visit them.

Anna and Artem were still building their cover. On Sept. 14, 2015, they married under their assumed names, Maria and Ludwig, a service in an otherwise empty building attended by two witnesses from Colombia, one of whom spoke to the Journal. The family marked birthdays privately, without inviting other children.

Nobody in the tiny circle of parents she interacted with seemed to notice anything odd about Anna’s accent or life story, other than a quiet sense of loneliness. Artem’s Spanish betrayed the lightest touch of something foreign, a trace he chalked up to his childhood in Africa. Forbidden from watching TV, their children ate healthy food and took swimming lessons.

In 2017, the two Slippers got a message from their handler. After more than a decade building their cover it was time to secure new visas and deploy for the next stage of their mission: Slovenia, in the heart of Europe.

First, there was a troubling wrinkle they would have to iron out to avoid detection. In the Argentine civil registry where their wedding record was stored, Anna had listed her mother’s nationality as Austrian, a falsehood Slovenia could easily check with its northern neighbor. In formal, immaculate Spanish, the young mother filed a petition for the Argentine registry to correct her mother’s origin from Austria to Mexico, whose birth records Slovenia would be less likely to consult.

But the change was detected by an officer processing their immigration paperwork in the Slovenian Interior Ministry—who found it unusual enough to note, though not suspicious enough to raise alarm. The visas for the Argentine family were approved and soon the Slippers were buckled into a trans-Atlantic flight, leaving behind only $21 in a Buenos Aires bank account and a credible-enough trail, if anyone ever cared to check.

The Boot, Pablo González, was already in Europe, traveling along Ukraine’s battle lines and spying on a circle of drinking buddies that widened from war correspondents to dissidents. What he didn’t know was that the U.S. and its allies were on his tracks.

Behind the passkey-activated doors that separated them from the rest of the CIA’s Langley headquarters, the officers at Russia House were piecing through a gathering stack of reports chronicling the double life of Pablo González.

For years the storied CIA division, formally known as Mission Center for Europe and Eurasia, had operated from the same warren of cubicles and offices as the agency shifted focus toward the War on Terror. But by 2017, the dozens of Russia analysts, officers and “targeters” scouring communications, official files and business records were tracing the contours of an expanding Russian spy network that included González.

Since 2014, Spain’s Centro Nacional de Inteligencia had been tracking the jet-setting reporter. In time, so were their counterparts at MI6 and in Poland, where he had been interviewing members of a new left-wing party and would begin dating a local freelance journalist.

For the spy catchers, this Boot was a bargain. The more he threw himself into missions, at times of his own volition, the more the Spanish and Americans could map his handlers, contacts, allies and command chain. Western officials studying the bilingual spy admired his natural talent and zest for the dangerous work, even as slips in tradecraft allowed them to track his network. One agency was able to find his documents uploaded onto a cloud service.

The hard-drinking war correspondent embodied an old spycraft dilemma: Once you catch a spy, should you intervene to stop their mission? Or silently follow them, to harvest more secrets? The CIA analysts in Russia House and their Spanish counterparts were inclined to keep watching.

He was becoming romantic with Zhanna Nemtsova, the grieving, exiled daughter of Boris Nemtsov, a Putin critic recently murdered near the walls of the Kremlin. She lent the Spaniard her father’s old laptop and he slipped the device’s email archive onto a thumb drive.

Then, on March 4, 2018, two GRU agents visiting England’s sleepy town of Salisbury smeared the nerve agent Novichok on the door of Skripal, the exiled Russian defector who had given the names of Russian spies to the British. The elderly ex-spy survived, but the would-be assassins’ careless discarding of a chemical weapon in a garbage bin ultimately killed a local mother of three. Her death galvanized a new round of attention on the GRU.

The U.K. pushed allies to expel more than 150 Russian diplomats in Europe and North America, largely intelligence officers working in embassies. Going forward, Russia would need to rely even more on its sleeper spies.

Before, intelligence agencies at times had brushed aside the dangers of Putin’s fixation with illegals. Now, they increased information sharing, scheduling rounds of face-to-face meetings with liaisons in embassies and check-ins over secure channels including the Battlefield Information Collection and Exploitation Systems created by NATO for wartime communication.

New personnel were posted to Russia House, tasked with the painstaking detective work of tracking the illegals’ flows of money, personnel and logistics. Analysts were surprised to see that the GRU was still acquiring passports through the old Cold War tactic of misusing a dead baby’s birth certificate. Soon, the CIA began identifying Boots.

One, Sergey Vladimirovich Cherkasov, who posed as Victor Ferreira, a Brazilian graduate student, was caught by a résumé slipup: The CIA noticed he had worked at a travel agency in Rio de Janeiro that they suspected was run by a GRU officer. By 2018, he was motorcycling each morning through Washington, D.C., studying American foreign policy and international economics at the Johns Hopkins School of Advanced International Studies. Though students puzzled over his odd accent, he ingratiated himself with professors unaware that their pupil was a GRU officer born in the Russian exclave of Kaliningrad.

Another Boot they found was Mikhail Mikushin, undercover as José Assis Giammaria, an eager student at Canada’s Centre for Military, Security and Strategic Studies at the University of Calgary. He was also struggling to convince his schoolmates that he truly was Brazilian. After what he claimed was a trip home to renew his visa, Giammaria passed out Rio de Janeiro souvenir bottle opener keychains to every student in his class.

What the Western pursuers didn’t know, and wouldn’t for years, is that two more spies had managed to slip right past them.

Now ensconced in a two-story home in the suburbs of Ljubljana, the quiet capital of Slovenia, the Dultsevs cut a low profile. They spoke to their children only in Spanish, and wouldn’t attempt even a sentence in Slovenian—the Slavic language was too close to Russian, and their native accent might poke through. Neighbors noticed little about the family who never entertained visitors and whose belongings, down to their white Kia Ceed sedan and the bike the husband pedaled downtown daily, all seemed designed to attract as little attention as possible.

The couple said almost nothing about their past except to blame crime in Buenos Aires for their move. Neighbors overheard the Dultsevs’ children playing in the garden, jabbering in Spanish, but the parents hardly ever stayed long outside. Anna was hardly ever photographed, with a rare exception: One Wednesday in late November 2019, she joined a Christmas decorating party in her daughter’s kindergarten classroom, flashing a strained smile over the caption, “A real Christmas spirit was in the air.”

For work, she had set up Art Gallery 5’14, an online company buying and selling mostly modern art. Hardly anyone in Slovenia’s small community of artists would remember anything at all about the unassuming mother of two whose office happened to sit a few steps from a European Union gas and energy regulator. The gallery claimed to work with 90 artists across the world and posted several images to its prolific social-media accounts almost daily. Strikingly, not a single picture showed her face.

Pablo González was flying closer to the sun.

Colleagues in the Spanish press corps had been gossiping over his ample supply of top-shelf cameras and expensive drones. He had been freelancing for U.S. government-funded Voice of America while airing Kremlin-sympathetic views on hourlong YouTube videos. He even attended a training hosted by Bellingcat, the open-source investigative outfit that unmasked Russian spies at a clip the analysts at Russia House often envied. His on-off romantic partner Nemtsova, the prominent Putin critic, had started to confide suspicions to other exiles about the well-connected reporter for small Spanish newspapers who took expensive weekslong trips to Ukrainian warzones.

One night, in November 2021, over beers in eastern Poland, he made a grand prediction to a small group of fellow foreign correspondents: Putin was about to invade Ukraine.

His cover unraveled three months later. Taking extended video footage of defensive positions along Ukraine’s eastern front, he spooked anxious soldiers bracing themselves for an impending invasion. Ukraine’s SBU intelligence agency immediately asked him to visit their Kyiv headquarters, where they questioned him for hours, probing his finances, career and where exactly he was born.

The same place as you, González shot back. The Soviet Union.

González was in a belligerent mood that night, downing drinks faster than other war reporters could keep up and laughing about the Ukrainian officers who’d scanned his phone and warned him to depart the country. He stepped out to call the Spanish embassy, which encouraged him to heed the advice. He flew to Istanbul to meet his handlers, then visited Spain for a brief stopover with his wife, before returning to Warsaw, reconnecting with his Polish girlfriend. He told journalists he’d left Ukraine because his Spanish ID was set to expire. All the while he was being tracked by British intelligence.

Just as Putin’s invasion moved ahead, the U.K. sent a tip to one of Poland’s top security officials: Did they know Pablo González was back in town?

One of the largest international arms transfers since World War II was under way at a small airport in Poland, where giant military cargo planes, loaded with equipment bound for Ukraine, were landing hourly. González, they would come to realize, had visited the airport, typing detailed notes on its layout and logistics on his new laptop.

Polish officers watched as González and his Polish girlfriend returned late on the night of Feb. 27, 2022, to the makeshift housing of a student dormitory near the border. The couple had been squabbling over his relations with other women. Shortly before midnight, a knock came at the door and officers filled the room, frisking them both then pulling González aside. He said nothing as they led him away.

The next morning, the Spanish woke up to learn the spy they’d hoped to keep studying had gone dark—the Poles hadn’t warned them.

In interrogations, González said he was worth a lot to the Kremlin and suggested they trade him for Alexei Navalny, Russia’s most prominent dissident, one of the officials dealing with the case said. Back in Spain, his lawyer and supporters launched a campaign saying he was guilty of nothing except journalism. González, who didn’t respond to emailed requests for comment, never admitted publicly to being a spy.

Neither the Kremlin, nor Russia’s foreign and military intelligence agencies, the SVR and GRU, responded to questions seeking comment.

On the other side of Europe, the CIA was delivering a tip to the officers of the Netherlands’ national security and defense intelligence agencies. The Brazilian Johns Hopkins graduate Victor Ferreira—Cherkasov, the GRU deep-cover officer—would soon be flying in to take an internship at The Hague’s International Criminal Court.

Russia House hoped the Dutch would keep watching him, but Dutch officials debating the stakes felt doing nothing could allow a Russian spy to access the building and email system of a court whose prosecutors had war crimes cases against Russia as far back as 2008.

Tall, with coiffed blond hair, Cherkasov walked through Amsterdam’s Schiphol airport in April to find Dutch authorities waiting to pull him aside then scan his devices. Like González, he’d been sloppy: Hidden on a laptop was his legend, or cover story, that ran just four large-text pages, much of it an elaborate explanation for his peculiar accent and why, unlike most Brazilians, he didn’t eat fish.

The Dutch deported him back to Brazil in the hopes that the government of President Luiz Inácio Lula da Silva would be a cooperative partner against Russian espionage. The country would hold him on a fraudulent passport charge. He arrived with a handwritten sign taped to his suitcase by the Dutch, a pun on São Paulo’s international airport code: “To GRU.”

José Assis Giammaria—GRU officer Mikushin—was next. The University of Calgary graduate was now a security studies researcher in Norway’s Arctic city of Tromsø, where police grabbed him on the way to work. Just like that, the West had rolled up three illegals in quick succession.

Yet there was an evidence trail pointing to another pair, who were proving far harder to track. The hunt began shortly after the February 2022 invasion of Ukraine, when Josko Kadivnik, the director of Slovenia’s Owl, received his invitation to fly to London.

Armed with a vague tip from MI6, Kadivnik built his investigative team slowly, inviting only the most trusted underlings into his office, framed by a metallic mosaic of an owl.

Most of the officers wouldn’t be told the full scope of their mission and were frequently rotated over months of slow policework. For the few who knew the truth, Kadivnik checked their pockets for loyalty: Select officers were given a gold coin emblazoned with an owl, a symbol of their tightknit club. If ever he found them without their coin, they would have to treat their colleagues to a round of drinks.

It isn’t clear how, in the needle stack of foreign-born residents, the officers slowly homed in on an Argentine family living at number 35 Primožičeva Street, a quiet suburban lane on the outskirts of the capital. Maria Rosa Mayer Muños had been flying to art fairs in London and Edinburgh, melding into an industry where laundered money and fraud mixed with high society. Was she legitimate? Slovenia’s national security adviser Vojko Volk, an erudite former ambassador to Italy, studied her paintings, noting that they all seemed unimpressive, like new-age art sold cheaply to clueless tourists.

Poring through the family’s bank accounts, investigators puzzled over whether the tuition of her children’s private British-curriculum academy was within their means. Her husband, Ludwig Gisch, had set up an online IT business selling domain names and cloud hosting, but it only had four followers on X, including the account of his wife’s business. He had promptly filed his tax returns, reviewed by the Journal, in 2021 claiming revenues of 40,000 euros alongside his wife’s 23,000.

Neither husband nor wife ever got so much as a parking ticket. Their operations security appeared nearly perfect, except for one error: Deep in their immigration records, Kadivnik could still see where the Interior Ministry had wondered, why had she changed her mother’s nationality from Austrian to Mexican? Now, the odd rectification added to a convincing body of evidence that the Argentines might not be who they said they were.

Owl began surveilling the gallerist, at times closely, other times backing off to avoid spooking her. Investigators opened their mail, hacked into their phones and discreetly trailed their car along Ljubljana’s cobblestone streets and past riverside cafes. The agency cross-checked information with Interpol and the CIA, eventually uncovering the real names, Anna and Artem Dultsev. Slowly, the couple’s mission revealed itself.

She was surveilling the director of an EU energy regulatory agency based in Slovenia, as it tried to rapidly wean the continent off Russian gas and help Ukraine avoid blackouts.

On trips across the visa-free Schengen bloc and London—for art exhibitions, ostensibly—Anna would meet sources. When she returned she’d ferry handwritten messages using an unhackable technique from the Cold War, placing them under a designated rock in a forest near the coast.

Owl would never know the full picture of what she was up to—but by Dec. 5, 2022, it was ready to strike.

The arrest would have to unfold without word reaching a single friend or neighbor of the couple, or any Russian sympathizer. Not even the U.S. ambassador was told more than she needed to know, as the local CIA station chief shuttled back and forth to meet the tiny set of Slovenians organizing the raid.

A cold fog was settling on Ljubljana, Christmas markets just opening their shutters, as a string of unmarked vehicles wove toward 35 Primožičeva Street where the Dultsevs were shepherding their children off to school. Kadivnik was watching in real-time on a feed filmed by some of his officers. He would extend the couple one courtesy before arresting them: Neither their daughter Sophie nor son Daniel would be home to watch their parents taken.

At 9:03 he gave the order and special forces burst through the windows so suddenly that Artem, hunched over a laptop, fell backward off his chair. He’d had no time to close the tabs on his screen, or shutter its secure communication to the SVR, which was still running. Screaming echoed through the home, as officers thundered upstairs, shouting “get down!” and bundling Anna onto the floor. She began to cry, claiming an injury, before returning to her feet, standing in silence. The arrest lasted only minutes and the couple left in handcuffs, their breakfast uneaten on the kitchen table.

Neighbors watched through their blinds, late into the night, as detectives searched the home and its yard, leaving with bags of money found in a secret compartment of the refrigerator, documents that included Anna’s forged Greek birth certificate, dozens of USB devices equipped with technology police had never seen before and Artem’s laptop, later sent to Washington for analysis.

Kadivnik delivered word to the CIA that the operation was complete. After nine months of high-strung policework, Slovenia had nabbed the first deep-cover spies in its history.

Three months later, in March 2023, Kadivnik slipped into a government building in Belgrade—neutral Serbian territory—to face the Kremlin’s top negotiator for prisoner swaps. The power imbalance was palpable.

Col. Gen. Sergei Beseda was known to some in Russia House as “the Baron” for his tailored suits and a cigar habit hinting at a youth as a KGB officer in Havana. He was wanted in Ukraine for allegedly encouraging former President Viktor Yanukovych to mow down demonstrators before he was toppled.

Now he was seated opposite Kadivnik with a question for Slovenia, a tiny state that won independence from communist Yugoslavia in the 1990s: Why are you doing America’s bidding? Most of all, he was there to deliver a direct message from the Russian president. Putin wanted his spies back.

On the phone with CIA Director Bill Burns, Kadivnik was nervous over what he was supposed to do with two elite Russian agents. Putin’s oldest ally, archhawk Nikolai Patrushev, had called to propose trading them for Slovenians in Russian prisons, but when Slovenia’s national security adviser insisted there were no Slovenians jailed in Russia, Patrushev paused then asked, menacingly: “Are you sure?”

The small country would have to be patient. All through 2023 and into 2024, Moscow and Washington haggled over which prisoners to trade. Poland held off bringing González’s case to a trial that, once it began, would make it harder to swap him.

The Dultsev children remained unaware their parents were charged with being spies, living in foster care, overseen by a female deputy Kadivnik appointed. Anna and Artem were allowed to speak to their children daily. But they begged prison guards to still call them Maria and Ludwig when their children came to visit. Watching the married spies, the Owl chief could tell that she was the more senior officer.

By July, President Biden was facing pressure to step down as his party’s presidential nominee. That month, Kadivnik got a call from the Slovenian prime minister’s office: a deal was coming together. The FSB and the CIA had inked an agreement at a clandestine meeting in Riyadh. The trade would take place on Aug. 1.

Russia would free a mix of dissidents, German prisoners, and three Americans: former Marine Paul Whelan and journalists Alsu Kurmasheva and the Journal’s Evan Gershkovich, sentenced to a combined 40 years on national-security charges they and the U.S. government denied. Washington and its allies would release eight Russians, including one held for ammunition smuggling, two convicted cybercriminals, and a hit man serving a life sentence for murdering an enemy of Putin in a Berlin park. The rest were Boots and Slippers.

At a July NATO summit in Washington, Biden’s national security adviser asked the Slovenians how the U.S. could thank the small country for its efforts. Slovenia wanted to build new nuclear plants. Could the U.S. help? Weeks later, Biden welcomed the Slovenians to the White House, where they discussed what Westinghouse Electric could do.

The plane that came to collect the Dultsevs from Ljubljana was a U.S. government jet. Kadivnik and a CIA officer would escort the family all the way to the exchange point in Turkey, and then, once they were rid of the spies, pop open a celebratory bottle of bourbon for their trip home.

Eleven-year-old Sophie spent the journey tapping away on a tablet. Her mother looked at her. At some point, during their flight to Moscow she would have to tell her children the truth: Her name was Anna Dultseva, a citizen of Russia, the country she had quietly served for almost half her life as a deep cover spy.