On a voyage to a major chess tournament, the world chess champion Centowic, Mario Adorf, hopes for a safe crossing, but the departure is unsettled by the belated arrival of an anxious passenger and the quiet presence of Bishop Ambrosse, Hansjörg Felmy standing nearby.
During the voyage, the passengers press Centowic to play a match, and he reluctantly agrees. His opponents appear poised to lose until the mysterious traveler — who claims to have just handled his first chess piece at any important tournament — intervenes and helps them salvage a draw. Centowic is astonished by the stranger, who says he has never before attended such a high-level contest.
The man turns out to be Werner von Basil, Curd Jürgens, an Austrian lawyer. With Bishop Ambrosse, he has concealed art treasures abroad to shield them from the Nazis who have just occupied Austria. At a party hosted by von Basil, Gestapo officer Hans Berger, Hansjörg Felmy, uses his girlfriend Irene Andreny to attempt to coax the hiding place’s location from von Basil. When she fails, Berger arrests von Basil that very evening and has him confined in solitary confinement, stripping him of nearly everything but the company of the guard who brings meals.
In confinement, Berger is pressured not only by Irene, who feels neglected, but also by his superior Hartmann, Albert Lieven, who wants the secret kept quiet. Von Basil pretends to cooperate, yet quietly resists, and even manages to pocket a book during a moment of questioning. Back in his room, he discovers the book is about chess matches, and with scarce resources he re-creates those matches using pieces of bread as makeshift chessmen. Even after Berger confiscates the volume, von Basil continues to play chess in his mind, rehearsing moves and possibilities as a way to endure.
Seeking help, von Basil turns to Bishop Ambrosse, hoping for mercy or leverage. Irene Claire Bloom pleads for von Basil’s release, but Berger dismisses her entreaties, and von Basil’s spirit frays under the rigors of isolation. Hartmann presses his own campaign to break the prisoner’s will, determined to expose or erase the truth von Basil guards about the art treasures.
As the narrative within the ship deepens, von Basil begins another tense chess encounter with Centowic, using the game as a vehicle to probe how much information he may have divulged during his solitary ordeal. The situation becomes emotionally charged when Irene returns to the scene and offers assurance that von Basil revealed none of his secrets. Her presence also marks a turning point: she survives the harassment from Berger and, in the eyes of the authorities, becomes a safer focal point for the human story behind the political danger.
In the end, the on-board confrontation mirrors the hidden conflict of the past: von Basil’s nerve and resourcefulness under pressure, the protective instinct of Irene, and the shifting power dynamics of Berger and Hartmann. The ship’s passengers witness a breakthrough of trust as von Basil and Irene’s bond deepens, showing that resilience and affection can endure even in the face of coercion and threat. The drama resolves not with a sensational revelation but with a quiet, steadfast affirmation: von Basil’s secrets remain protected, Irene’s courage remains intact, and the strange, puzzle-laden journey toward the tournament is tempered by a newfound trust that carries them toward a more hopeful horizon.
