Martin Rauch leaves his home in East Germany to spy for the HVA undercover in the West German army as Moritz Stamm. The East German HVA is concerned by Reagan's "Evil Empire" rhetoric and American military plans in West Germany. When an opportunity for one of their assets presents itself, high up in the Bundeswehr, they quickly need someone very young. So Lenora Rauch sends her nephew, Martin Rauch to West Germany against his will. In Bonn, en route, he receives intensive training from HVA field operative Tobias Tischbier, and arrives at the army base in the Eifel under a new identity: Officer Moritz Stamm. His job is to collect intelligence on NATO plans to station Pershing II nuclear missiles in West Germany, as aid to a General Edel. Also, in the process, to befriend Edel's rebellious children, the angry Alex and the beautiful Yvonne.

Moritz completes a far more dangerous mission and is beginning to enjoy his life in the West. While General Edel meets with NATO colleagues to discuss the Pershing II missiles deployment, Moritz is ordered by Tischbier to break into Hendrik Mayer's hotel room and steal a top secret security report. He refuses to do so until Tischbier promises to help his mother, Ingrid, who is suffering from diabetes back home in East Germany, where treatment is scarce. When Moritz finally steals the NATO report, his superiors at the HVA in East Berlin cannot read it because it's not saved on paper—but on a floppy disk. This technological hiccup turns into a humiliating struggle to keep up in the dawning era of the computer, a key example of the diverging paths of Communism and Capitalism.

While at a NATO conference in Brussels, Moritz gets his first "Romeo" assignment: to seduce the head security analyst's secretary, Linda. General Edel and his new aid bond on a trip to Brussels to meet with the top brass. Lenora emerges to tell Moritz that his mother needs a kidney transplant. She takes his blood to see if he might be a match. Back in East Berlin, Annett moves in to take care of Ingrid, at Lenora's suggestion, and reveals that she is pregnant with Martin's baby. When Moritz reconnects with Linda, a secretary he met earlier in Bonn, he sleeps with her and successfully installs a microphone in her desk at NATO. Moritz manages to connect the HVA Headquarters with the office of the top military security analyst at NATO Headquarters. It is the first time he pulls off such a complex spy manoeuvre successfully. His star keeps rising.

When the bug is found in Linda's desk, all NATO is in high alert. Moritz must cover his tracks by any means necessary. The bug is discovered in Linda's desk in Brussels just as she arrives to visit Moritz in West Germany. Moritz scrambles to turn her loyalties while under interrogation by NATO brass about their relationship. Back in the Eifel, as Linda figures out Moritz's true identity, she runs. Moritz follows but the HVA is way ahead of him. Moritz is forced to recognise the dark reality of the organisation he is working for and after a brief honeymoon with tradecraft, his job becomes a terrifying trap.

Tischbier arrives at the commune and informs Martin that his mother will have her kidney transplant but he's the donor; Martin must deliver a package to a mysterious man on his way to East Berlin.

When Moritz returns to his undercover life in West Germany he is drawn into Alex Edel's fatal plans; Alex Edel takes General Jackson hostage and forces him, at gunpoint, to film a seething denouncement of US military plans in Western Europe.