The story’s protagonist, Rollo Martins, is a young British writer whose genre is Westerns. He goes to Vienna at the request of his childhood friend, Harry Lime, to write about Lime’s work with refugees—but upon arriving in the city hears that his friend is dead. Martins is impulsive, particularly with women, whom he tends to refer to as “incidents” who force him to flee cities to escape them. In addition, Martins drinks heavily, which contributes to his unhappy love affairs. Somewhat naive and a loyal friend, Martins refuses to accept an official’s suggestion that Limes was involved in criminal activity. Martins is cynical about law enforcement and isn’t shy about standing up to authority or avenging Lime’s death, as if Martins sees himself as the hero of a Western.

For all his impulsivity, Martins also has cunning and skill. He successfully conducts an amateur investigation, collecting evidence that the police can’t and interviewing Lime’s associates and his neighbor. The police detective, Calloway, considers him to have a dual nature—ridiculous and reckless while also effective and ”steady, careful”—and therefore begins to see him as “dangerous.” Martins takes advantage of a naive cultural worker, Crabbin, who has mistaken “Buck Dexter” (Martins’s pen name, which he used on the flight manifest) for the far more famous Benjamin Dexter.