France, 1935. Englishwoman Kate Farrant works for industrialist Erich Krogh, whose mistress she is. She reunites with her brother Tony, who has quit yet another job. Kate is returning to Germany; she persuades Tony to come with her, saying that Krogh could find him work.
In a Berlin bar, Tony gets talking to Minty, an English journalist, Minty. Minty hopes Tony can get him information on Krogh, for which he offers to pay. At a formal meeting, Krogh suggests Tony have a job liaising with publicity; Tony eagerly says he's already made contact with local journalists, which horrifies Krogh.
While Tony flirts with Liz Davidge, an English girl he has met, Krogh discusses his worries with Kate: his business is failing, he needs investors, and the only option left to him verges on fraud. Tony wants to have sex with Liz but doesn't know anyone in town, so they visit Minty. When Minty says he has to leave for work, Tony asks if he and Liz can stay. After they've had sex, she asks if he'll return to England with her, but he can't because of his job.
Kate tells Tony she's marrying Krogh so the three of them can be together forever, as she's always wanted. Krogh calls to say he is throwing a party at his lakeside villa and has invited a Reichsminister. He wants to leave the country, probably for England. When he understands Krogh's business plans, Tony is shocked: > It's a swindle! > Kate emphasizes the importance of the press not finding out.
Tony sees Liz off at the airport. Minty is there, spying on them. Tony promises Liz that he'll abandon his job and rejoin her in England within the week. He sees Minty and invites him for a drink. Tony tells Minty about his plans to return to England, the looming party, and Kate and Krogh's marriage. Minty instantly scurries away. Krogh's assistant Haller tells Krogh that the Reichsminister suspects something (Krogh's firm have been buying their own stocks) and will stop Krogh leaving the country.
Idling at Krogh's offices, Tony leafs through a file. When Kate enters, she grabs it and warns him to keep quiet. Tony tells her he's returning to England; she correctly intuits it's because of Liz: > I can't appeal to you like she can! <
Knowing that he'll be broke when he returns, she gives him money, wondering why she can refuse him nothing.
At the party, guests get increasingly drunk on Krogh's champagne, while Krogh and Haller play cards with Nazi bigwigs: the Reichsminister asks Krogh "for a little informal chat tomorrow".
Fromm, a Jewish acquaintance of Krogh's, appears at the villa. His son has been arrested and he wants an audience with Krogh. Haller beats him and throws him out. Tony sees this and tries to intervene, though Kate restrains him. Tony rants angrily against Krogh, mentioning that he has falsified business records. Kate impulsively silences Tony by kissing him on the lips. Haller witnesses all this.
The following day, Kate reads in an English-language newspaper that she's marrying Krogh. Krogh knows this is because Tony has told Minty. He thinks Tony's departure "inconvenient" but believes he can stop it.
Tony writes Minty a letter. When Kate enters, he rapidly hides it. On their way back from the disastrous meeting with the Reichsminister, Krogh and Haller discuss ways of stopping Tony returning to England. Haller suggests getting him into a card game and making sure he loses, so that he won't have money to travel.
At the game, Tony chats about his impending departure as Haller and Krogh exchange glances. Everyone folds except Haller and Tony, who while talking about his terrible hand has been practicing a poker face: he has a straight flush. Tony collects his winnings and walks to the station. When he stops to light a cigarette, he sees Haller behind him.
Haller returns to the villa, looking shaken. As dawn breaks over the lake, Tony's body can be seen floating.
Tony's letter arrives at Minty's lodgings, but before he can open it, Haller arrives. He bribes Minty, whose newspaper then runs a piece saying Tony's death was accidental. Kate packs her belongings and walks out on Krogh.
