Based on a novel by W. R. Burnett, a new doctor in a small town treats a gangster and a woman wounded in a bank robbery.
Dr. Ginder (Robert Barrat) describes a bank robbery by Red Bastian's gang. Dr. Lee Caldwell (Paul Muni) tells Dr. Ginder he has no paying patients because of him. Lee's friends from Chicago visit him. Lee recalls how a quarrel with his fiancé led to a car accident and her death in spite of his surgery. Since then he has nervous hands, and he won't go back. Ma Ganson (Helen Lowell) tells Lee they don't have money to pay the grocery bill. Red Bastian (Barton MacLane) with a gun tells Lee to treat his gun-shot wound. He leaves him $100 and tells him to keep quiet. Lee meets banker Ben Suggs (Raymond Brown). Lee makes a call on the banker's daughter Caroline Suggs (Grace Stafford), saying it's her nerves.
Josephine Gray (Ann Dvorak) hitches a ride with Red and his gang. They rob a bank with much shooting, as she tries to run away. A police car is unable to catch the robbers. Lee looks at Josephine's shoulder wound and takes her to his home for treatment. Dr. Ginder brings a crowd and the sheriff; Lee won't give her up, and the sheriff entrusts her to him. After a vigilante meeting, Lee is asked about typhoid. Lee invites Josephine to stay, and he sends the photographers away. She says good-bye; but he brings her back. Ben Suggs and Caroline invite Lee to dinner. Red's men take Lee blind-folded to treat Red's inflamed arm. Bob Catlett has been drinking a tonic for typhoid and is drunk. Red wants Josephine, and Lee refuses his money.
The FBI sends Greer (Henry O'Neill) after Red Bastian, and he learns from Ben Suggs that a $100 bill came from Lee. Suggs calls Lee to warn him. Lee discovers that Red's men took Josephine. Red tries to be nice to her and bullies his girlfriend into cooking for them. Greer questions Ma Ganson, and she pleads for Josephine. Lee goes to Red and says he is in trouble with the law, denying he wants Josephine. Greer has the sheriff surround the house with armed men. Lee says Red's temperature is 103. He suspects typhoid from the water and gives himself a shot. Then he vaccinates Red's men and finally Red. Police close in. Red's gang passes out, because Lee gave them dope. Red starts shooting, and the police fire back. Eventually Red passes out. Lee is acclaimed a hero and is given a party, but he would rather have a private ceremony with Josephine.
The surly Lee got his name from reading Plato, and he is often frank about who he does not like. Yet he is generous to others and wins people over by heroically catching the gangsters with his cleverness, showing a sharp contrast between his method and the violence of guns.