For four decades in East Germany, the dreaded Stasi secret police snitched on counter-revolutionaries, tortured political prisoners, and generally out KGB-ed the KGB. Daring to find a good German in the Stasi ranks, The Lives of Others writer-director Florian Henckel von Donnersmarck builds a powerful thriller around one agent’s clandestine humanity. At the beginning of the film, Stasi captain Gerd Wiesler’s unflinching faith in socialism is a blankly vicious thing: Students learning the art of interrogation from him murmur uneasily as they listen to a tape of a prisoner breaking down, but Wiesler (Ulrich Mühe), silencing them with a word, encourages them to pay closer attention. And when he begins monitoring the wired apartment of playwright Georg (Sebastian Koch) and his leading ladyngirlfriend Christa-Maria (Martina Gedeck), Wiesler exhibits a palpable glee when he slides his headset over his ears. But there’s trouble in his post-Stalinist paradise—a powerful party minister who has fallen for Christa-Maria puts Wiesler on Georg’s trail to find an excuse to eliminate the playwright as a romantic rival. Wiesler secretly rebels: He alters his surveillance reports when Georg is drawn into a revolutionary act and begins to serve as the couple’s guardian angel. Mühe (who grew up in East Germany) flawlessly portrays Wiesler’s emotional isolation, and he makes his improbably fast radicalization feel inevitable. Von Donnersmarck’s script depicts the captain’s disillusionment with the Stasi as a product of his belief in socialism—Wiesler signed on with the police force to serve as his government’s “shield and sword,” but, when a corrupt leader goes too far, he instinctively and immediately switches sides. Pulling off what’s essentially a Pinocchio story—an automaton learns to become human—is a feat of acting; fumbling through a pathetic coupling with a prostitute, passing up an opportunity to report a neighbor who has identified him as a Stasi agent, or disappearing into a stairwell when Georg passes by, Mühe conveys anxiety through the simplest gestures. It’s a virtuosic performance, and though the film’s overlong ending threatens to undo the intricate emotional architecture, The Lives of Others comes through unscathed. Often compared to The Conversation, Francis Ford Coppola’s 1974 film about the existential life of a private detective, The Lives of Others does its American antecedent one better; where Coppola became mired in noir, von Donnersmarck celebrates one man’s quiet redemption. One of 2006’s best movies (and fully deserving of its Oscar nomination for best foreign film), The Lives of Others traffics in a virtue too many art-house directors fear: optimism.