In 1971, the British photographer Richard Bryant, Patrick Jordan, plunges into the icy depths of a mountain lake called Finstersee and pulls up a heavy box. Two locals close in, demanding to know where the chest is hidden. When Bryant refuses to answer, a brutal strike sends him crashing to a rock, and his fate is sealed by the cold, unforgiving water.
The story widens in Salzburg, where the US lawyer Bill Mathison, Barry Newman, vacations and stops by Bryant’s shop to inquire about a book on Austrian mountain lakes on behalf of publisher James Newhart. Bryant’s Austrian wife Anna Bryant, Anna Karina, hands Bill correspondence from Eric Yates, Newhart’s representative in Zurich, along with a countersigned cheque for the illustrated volume. The two men’s paths cross with quiet tension as the murky web of espionage begins to unfold.
Anna’s brother Johann Kronsteiner, Klaus Maria Brandauer, receives a warning call from Felix Zauner, Wolfgang Preiss, a family friend who insists Bryant’s death was not an accident. Johann travels to identify the body at an inn near Finstersee, where the innkeeper, Grell, Helmut Schmid, reveals himself as the elder of the men who confronted Bryant. The sense of a larger conspiracy grows as the hunt for truth draws Bill deeper into a charged European landscape.
Not far from Bryant’s shop, Bill becomes aware of a tail—two men shadow him through Salzburg. To lose his pursuers, he hops into a hackney and is driven through winding streets, even as a heavyset stranger with a moustache follows. On a tour of the fortress of Hohensalzburg, Bill confirms the pursuit and finally sheds the threat. It’s there that he meets the young American Elissa Lang, Karen Jensen, a woman who seems at once open and dangerous. Their conversation uncovers a tangled shift of loyalties: Elissa works for Zauner and, as it turns out, is also feeding information to Lev Benedescu, Mischa Hausserman, a Russian agent, signaling that she is a double agent rather than a simple tourist.
As the threads tighten, Anna confides in Bill that Bryant and Yates once worked for the British secret service, and she suspects that Bryant’s death is connected to something far larger. She explains that Yates has also died under suspicious circumstances, and she fears the chest may be the key to dangerous knowledge. Meanwhile, Elissa infiltrates Bryant’s shuttered shop, steals the photos from Finstersee and the related correspondence, and vanishes into the night. Bill and Anna discover the theft and later confront a dead man in an alley—one identified by Anna as Bernard Dietrich, Zauner’s deputy.
At Finstersee, Johann is stalked by two neo-Nazis, one of whom is Anton, Udo Kier. They corner him, but he locates the chest and hides it at the home of his girlfriend, Trudi Seidl, Elisabeth Felchner. Bill takes Anna to his hotel for safety, while Johann’s search for the missing chest continues. The next day, Johann’s arresting sense of danger increases when an Israeli visitor appears to have offered to pay handsomely for the chest, underscoring its immense value.
Bill meets with Chuck, a CIA agent, Joe Maross, who has been in contact through Newhart. On their way to a meeting, Bill is again tailed, and Chuck arranges for the moustached pursuer to be shot by an assassin. Chuck explains that the CIA had collaborated with Yates, another double agent, adding another layer to the already intricate web of espionage. The heart of the mystery emerges: the chest contains documents listing former Nazis who have remained active and who are either embedded in Western institutions or used by Western intelligence. The Russians, too, have found a similar chest in Czechoslovakia, and the value of these lists becomes crystal clear.
Johann returns home only to be captured by the neo-Nazis who want to know where the chest is hidden. Anna and Bill worry for him and plan to meet Trudi that evening, only to find Zauner’s car in sight. Zauner explains that he knows where Johann is being held, but Elissa appears, forcing a tense standoff. Zauner’s interest in the chest is personal: his name appears on one of the lists, and his past as a Nazi informant—used to protect his wife from deportation—has been exploited by the KGB, driving his cooperation with Elissa.
The finale accelerates as the group heads to the hideout. Elissa tries to manipulate Johann’s captors to reveal the chest’s location, while Zauner and Bill race to reach the scene before more bloodshed. In a dramatic confrontation, Anton shoots Zauner, and Bill, wielding calm resolve, disarms the neo-Nazis and rescues Johann. Anna and Bill then escape Salzburg together, driving off in Zauner’s Porsche as the mystery of Finstersee closes behind them, leaving behind a trail of moral ambiguity, political intrigue, and the fragile cost of truth.
