Guy Van Stratten, a small-time American smuggler working in Europe, seeks out a Munich resident named Jakob Zouk to warn him about a plot against his life. Zouk is fatally ill and receives the news with apathy, so Stratten explains his personal reasons for wanting to keep Zouk alive. His narrative is accompanied by scenes in flashback.
Stratten’s story begins in Naples, where he gets a tip that Gregory Arkadin, a famous international oligarch of Russian heritage, possesses a dark secret centered on the name “Sophie”. Stratten and his girlfriend and accomplice Mily travel to Arkadin’s castle in Spain, hoping to use this meager information for blackmail. By striking up a friendship with Arkadin's daughter Raina, seemingly the only person for whom Arkadin feels affection, Stratten gets himself invited into the castle.