Spying is the art of betrayal. If we accept it as the second oldest profession in the world (there were spies in the Bible and in the records of ancient China and Mesopotamia), then it follows that betraying is as much a time-honored habit as a natural instinct, as elemental and as universal as hating or loving. John le Carré recognized the link. “Love,” he explains in The Looking Glass War, “is whatever you can still betray.”

Such betrayals have always been enacted within a shady, murky realm full of smokescreens, obfuscations and denials. Despite attempts at transparency after spies came in from the cold, today’s world of spying feels like an even grayer area than ever before—to the extent that it is hard to define what constitutes “betrayal.” For some, the likes of Julian Assange, Edward Snowden, and Bradley Manning are perfidious, secret-leaking traitors who should rot in jail; for others they are principled, whistleblowing heroes who should not only be free but also applauded.

Some decades earlier, it was all so much more clear-cut. Spies were unmasked, branded traitors, and punished accordingly. Jim Nicholson, the highest-ranking CIA officer to be convicted of spying, is currently serving a 23-year prison sentence at a Federal correctional institution. Adolf Tolkachev, one of the most productive Soviet sources for the CIA during the Cold War, was snared by the KGB and executed. Few dispute that Nicholson got what he deserved. In Russia, Tolkachev is only mourned by his son.

Two new books shine a light on the daring, game-changing exploits of both men. In The Spy’s Son, investigative reporter Bryan Denson describes Nicholson’s rise and fall, and that of “the son who joined him in the family business of espionage.” In The Billion Dollar Spy, Pulitzer Prize-winning author David E. Hoffman shows how Tolkachev was driven not by greed or ideology but vengeance to pass thousands of secret documents to the U.S.

The Spy’s Son opens in Eugene, Oregon, in the fall of 2008 and introduces us to Nathan Nicholson, a 24-year-old college student. For the past two years, Nathan has divided his time between studying, visiting his father behind bars and, at his parent’s behest, couriering top-secret messages to Russian agents. So far this chip off the old block has made clandestine deliveries in San Francisco, Mexico City, and Lima. His next port of call is Cyprus. He flies there, passes information to his handler, collects $13,000 for his trouble, and is instructed to meet again one year later in Slovakia. Shortly after arriving back home he is jolted from the fog of jet lag by two Feds pounding at his door. Has his lucky streak come to an end?

Denson leaves us with this cliffhanger and branches off to tell Jim’s story. He joins the CIA, enjoys a series of foreign postings, and rises through the ranks. Crunch time comes in 1994, when he is tasked with meeting the rezident or station chief of the SVR, the KGB’s successor, in Kuala Lumpur, with a view to coaxing him to work for the CIA. Instead, Jim offers his services and changes sides. For much needed cash he agrees to give up the identities of hundreds of new recruits at the CIA’s training center, The Farm. A double life begins.

In time, Denson weaves a third strand into his narrative, and in so doing answers what Le Carré called “the oldest question of all” in Tinker, Tailor, Soldier, Spy: “Who can spy on the spies?” Enter a small, top-shelf team of FBI spy-catchers to sift and identify any CIA bad apples. Jim raises suspicions among counterintelligence agents who notice he has been depositing more money than he earns, and a polygraph operator smells a rat when Jim keeps flunking the same two questions about having and hiding contact with a foreign intelligence service. Through intensive undercover trailing and electronic eavesdropping the scope of Jim’s duplicity is revealed and the net closes in on him.

Denson skillfully traces Jim’s journey from U.S. intelligence officer to convicted spy to U.S. prisoner. But neither disgrace nor incarceration stymies Jim’s illicit dealings with the Russians. Adoring and impressionable son Nathan is talked into smuggling out his father’s jottings and passing them on to the head of security at a Russian consulate. Prison visits are spent with Jim furtively teaching Nathan rudimentary tradecraft and slipping him more transcribed accounts of accumulated wisdom and know-how. “And so it was that in the middle of October 2006, a dozen years after Jim began spying for the Russians, he sent them his youngest son.”

Jim was not to know that the son he was training to be his intrepid envoy would in due course be a lamb led to the slaughter. Indiscretions become blunders, which once again put the FBI on the scent. At this point a wearying sense of déjà vu could have crept into the story, but Denson keeps things fresh by regularly stoking the tension, whether by recounting the frantic monitoring of cryptic phone calls and correspondence between father and son, or the cat-and-mouse game of evasion and pursuit in exotic locales. Just when we come to believe that Nathan’s arrest might herald cathartic release, Denson fills the last stretch with the court case and an agonizing dilemma: Will Nathan cut a better deal for himself by testifying against his father?

There are numerous instances, not least this highly charged denouement, when we want to take Denson to task for heedless sensationalism. We hold back, however, on remembering that his story is factual, that this soap-operatic melodrama actually happened. What especially beggars belief is not rookie Nathan’s operational slip-ups but those of his father, the old pro (stepping into a car with Russian diplomatic plates; copying a trove of classified files to his laptop). A different kind of bad is Jim’s naivety. When he isn’t sitting in his cell learning Russian and dreaming of a new-start on his release, he is cobbling together a hare-brained escape plan for Nathan to propose to his handler—one involving a Russian extraction team in a helicopter plucking him from the prison’s outdoor recreation yard and transporting him to a waiting submarine.

Despite the careful plotting and well-calibrated excitement, Denson’s narrative is let down in places by bizarre phrasing (“He had flown home that fall with an honorable discharge and a duffel bag of despair”), bland repetition (we are constantly in the “bowels” or the “bosom” of buildings), and known fact masquerading as sharp insight (“Swiss banks are spectacularly secretive”). And then there is his curiously erratic style. Chapters begin with portentous epigraphs from the Bible, Sun Tzu or T.S. Eliot, then cover the latest grim, tense or fantastical developments in prose that alternates between boardroom serious and locker-room familiar. After the Cold War, Denson informs us, Russian spying would be “a grudge rematch against the West, which had quietly knocked their dicks in the dirt.” In court Jim sits with calm resignation, “not eye-fucking the prosecutors.” Spy-catcher Maguire “took his seat, his sphincter already tight enough to crush walnuts.” There is one notable occasion when we are told that “Maguire now wanted the narcissistic prick behind bars.” But Denson is ventriloquizing Maguire; this vitriol is Denson’s, and when it overspills it pollutes what is otherwise a cool, neutral reportorial tone.

Perhaps what is most jarring is the book’s title. Simply stated, The Spy’s Son is a misnomer. Denson serves up a cautionary tale of how the sins of the father are visited upon, and then committed afresh by, the son. As such, in this double-whammy of betrayal, Jim and Nathan deserve joint top-billing.

Less contentious, more aptly titled, and focusing on only one traitor (this time betraying the Soviet Union) is Hoffman’s The Billion Dollar Spy. Drawing on numerous operational cables between CIA headquarters and the Moscow station from 1977 to 1985, Hoffman shows how a Soviet engineer who had grown increasingly disgruntled with the Soviet state sought to dismantle it by selling secrets to the other side.

Unlike Denson, Hoffman doesn’t so much cut to the chase as take slow, leisurely steps. But this is no bad thing. His early chapters measure the political temperature of the fifties and sixties and chart two big breakthroughs for the CIA in Moscow: securing Pyotr Popov and Oleg Penkovksy, two officers in Soviet military intelligence, to spy for the U.S. However, following both men’s exposure and executions and their American handlers’ expulsion from the country, a long drought set in, whereby the only intelligence trickling into the CIA was of the low-grade variety peddled by small-fry Soviet agents.

That all changed in 1978 when the chief of the CIA’s Moscow station was handed an envelope by a man on the street. In it was jaw-dropping documentation of Soviet radar and avionics capabilities. The haul was too good to be true, and prompted senior spooks to suspect a trap. The man was rebuffed for more than a year and a half, but his perseverance won the day. After checking out his bona fides and evaluating his intelligence, the CIA realized that their man, Adolf Tolkachev, was the real deal and the most prized source they had had to date.

Tolkachev was well aware of his value and so named his price. As the quality of his intelligence rose, and the risks he took to get it became greater, he adjusted his rate of remuneration accordingly. Hoffman recounts a misunderstanding over his request for a six-figure sum. “I had in mind not a figure with six digits,” Tolkachev explains in a note to the CIA, “but a number with six zeros.” The CIA had never paid an agent on such a scale before, but when they calculated that his intelligence saved them at least $2 billion in research and development costs, his million-dollar salary suddenly justified itself. Tolkachev, Hoffman writes, “was the Moscow station’s crown jewel of human source intelligence collection.” On the other side and at the opposite end of the spectrum, poor old Nathan Nicholson was only able to glean a paltry $47,000 from the Russians.

Hoffman takes us through the last years of the Cold War, from Reagan entering office (and ramping up activism against the Soviet Union) to the arrival of Gorbachev and the prospect of a thaw in American-Soviet relations. We hear of Tolkachev’s covert meetings with his case officers, his updated wish-lists (Led Zeppelin and Alice Cooper albums for his son; samizdat books by Solzhenitsyn, and a cyanide capsule for himself), and in a suspenseful climax learn how he was betrayed from within the CIA. Instead of wrapping up with Tolkachev’s capture and tragic fate, Hoffman appends a fascinating epilogue which fast forwards to Operation Desert Storm in 1991 and demonstrates the way Tolkachev’s decade-old intelligence helped the U.S. Air Force down Soviet-built tactical fighters in aerial combat over Iraq.

In one chapter Hoffman rewinds to fill us in on Stalin’s show trials and Great Terror. We locate the origin of Tolkachev’s deep antipathy to the Soviet state, his disdain of the “impassible, hypocritical demagoguery” of Khrushchev’s party politics, and come to sympathize with his later decision to injure the whole system by betrayal. This backward step will be, for some readers, either an elucidating offshoot or a meandering deviation. Whatever the case, once Hoffman brings Tolkachev back to the present, we feel once again in thrall to the momentum of his main, thundering narrative.

It is becoming something of a cliché to refer to a riveting factual or autobiographical history as being “like a thriller.” But at the risk of continuing this trend, both of these spy books are genuinely, at times compulsively, gripping. Denson’s is wilder, brasher, gutsier; Hoffman’s is more sober, more chilling, and brimming with cloak-and-dagger intrigue. Both are meticulously researched and replete with authentic and arcane tradecraft. And yet while Hoffman supplies the expected dead drops, brush passes, and false flags, Denson’s spy-speak teaches us a new language. Beholding access agents or plank holders dry cleaning, using accommodation addresses, or hanging out the shingle puts us in mind of Le Carré’s lamplighters and scalphunters coat trailing, raiding reptile funds, or plotting mailfist jobs.

At the end of The Billion Dollar Spy, we are told that Tolkachev’s wife, Natasha, remained angry after her husband’s death about the fact that he carried on his spying despite assuring her he would stop. It wasn’t the ethics of espionage she objected to, rather the danger to the family. Jim Nicholson knew the risk involved with his treachery but then for some unfathomable reason went on to groom his son to fill his shoes. If we cut through the intricate webs of deceit and swaths of skullduggery, we find in both informative and captivating books two very different fathers—one reckless, one selfish—each attempting to do the right thing for those who mattered most. In shadowing them, Denson and Hoffman home in on what Graham Greene called “the human factor,” tracking motivations, sifting loyalties, and assessing the damage a spy does not just to his country but also his family.