Just released from prison, John Müller hatches a plan to pull off a daring heist at Rocky Stansyck's illegal casino. The robbery goes badly, and the mobsters capture several of Müller's men, forcing them to identify the rest before killing them. Rocky Stansyck has a fearsome reputation for tracking down his enemies, no matter how long it takes, so Müller decides to vanish and hide.
He takes an office job recommended by his law-abiding brother, Frederick, but quickly discovers that “working for a living” isn’t his style.
A chance encounter with the dentist Dr. Swangron reveals that Müller looks precisely like a psychoanalyst who works in the same building, Dr. Bartok, the only difference being a large scar on the left side of the doctor’s face. Seizing the opportunity, he begins studying Bartok, even slipping into his office to examine the records. He is spotted by Bartok's secretary, Evelyn Hahn; she mistakes him for her employer and even kisses him, but quickly realizes he is an imposter. He persuades her to go out with him, though she remains embittered and claims to have given up on love.
Müller sets out to impersonate Bartok, leveraging his own medical training and a photograph of the doctor as a guide to cut an identical scar on the right side of his own face. After he murders Bartok and prepares to dump the body in the river, he discovers that Bartok’s scar should be on the left side and that the photograph was printed with a reversed negative. He forges ahead anyway, and, aside from the cleaning lady’s suspicions—which he manages to lull away—no one notices the discrepancy, not even Evelyn or Bartok’s patients.
Müller then learns he has a girlfriend, Virginia Taylor, and that they frequent Maxwell’s, a high-class casino. It also turns out Bartok has been losing heavily.
When Frederick Müller tries to reach his brother, the trail leads to Bartok. The scar convinces Frederick that the man he sees is merely a lookalike. Evelyn, now more suspicious, reveals that John Müller had said he planned to go to Paris. Frederick tells “Bartok” that his brother no longer has to hide, because Stansyck has been convicted for “income tax problems” and is scheduled to be deported.
Afterward, Evelyn realizes that Müller has impersonated Bartok and killed the real doctor. Although he admits it, she does not turn him in, instead purchasing a ticket to sail to Honolulu. Müller hopes to go with her, but she remains skeptical of his generosity. He arranges for other doctors to take care of his patients and heads to the dock. There, he is intercepted by two men who want to discuss Bartok’s $90,000 gambling debt. When Müller tries to break away, they fatally shoot him. Evelyn sails away, unaware that Müller intended to keep his promise to her.
