Simon Templar is a Robin Hood-like figure known as the Saint – plausibly from his initials, but the exact reason for his nickname is unknown. Blessed with boyish humour, he makes humorous and off-putting remarks and leaves a "calling card" at his "crimes," a stick figure of a man with a halo over his head.
Police Lieutenant Martin, an officer leading the fight against New York gangsters, is killed. Jake Irbell is arrested and charged with his murder, but has to be released when prosecution witnesses are either coerced into changing their testimony or simply disappear. A civilian crime commission demands action of the police commissioner, but he has no fresh ideas. William Valcross (Frederick Burton (actor)), a respected leading citizen and member of the commission, suggests they resort to drastic measures and recruit Simon Templar (Louis Hayward), the "Saint", a British amateur Detective with a reputation for dealing with criminals outside the law. The commissioner reluctantly agrees to give the Saint free rein to do what he must.
While dancing at a New Year's party, the Saint spots an agent of Valerie Travers preparing to shoot someone, so Templar guns him down first at the stroke of midnight. Templar is placed by witnesses at the scene, so the San Francisco police request the assistance of Inspector Henry Fernack (Jonathan Hale) of the NYPD. Before Fernack can leave, the Saint arrives in New York and accompanies him to the West Coast.
The Saint returns to London and with the help of an American pickpocket and a beautiful adventuress breaks a counterfeiting ring.
An enigmatic gang leader known as "The Boss," who is a dead-ringer for Simon, puts "The Saint" under suspicion of murder.
Inspector Fernack is framed by a cartel of five gangsters and Simon does his best to prove it before all the conspirators are murdered by a mysterious killer.
Inspector Fernack asks Simon to watch over an old friend who's carrying $200,000 worth of postage stamps, but the friend is killed, and the stamps stolen.
The last words uttered by by a conscience-stricken crook dying on the Saint's doorstep lead the detective in pursuit of gold smugglers and the master crook known as the Tiger.