The rogue (George Sanders) who would later call himself Eugène François Vidocq is born in a prison cell, the twelfth child of a woman who steals a loaf of bread each time she needs shelter to give birth. As the boy grows into a man, he is constantly in and out of jail. As the story begins, he and his cutpurse cellmate and associate, Emile Vernet (Akim Tamiroff), escape using a file hidden in a birthday cake provided by Vernet's aunt Ernestine.
While making their way to Paris, they are hired to pose for a painter (Fritz Leiber), Vidocq as Saint George and Vernet as the dragon. As the church painting nears completion, the pair steal the horse on which Vidocq is posing.
In Paris, Uncle Hugo (Vladimir Sokoloff), the head of Vernet's criminal family, decides the safest place for the fugitives is in the army. He has a forger relative provide Vidocq with a fake commission as a lieutenant. After two years, the pair leave the army. Returning to Paris, Lieutenant "Rousseau" encounters a singer named Loretta (Carole Landis). She is intrigued with him, while he is more attracted to her ruby garter. Accompanying her when she goes to meet her boring admirer, Vidocq manages to steal the garter.
As Vidocq and Vernet make a detour around the church adorned by their likenesses, they come across the jewel-laden Marquise De Pierremont (Alma Kruger). Vidocq wrangles an invitation to her chateau after retrieving her pet monkey from a cemetery (where he also claims to be a relation of a Vidocq buried there). He is a bit alarmed when he discovers that his intended victim's son-in-law is the Minister of Police (Alan Napier), but also enchanted by the official's daughter Therese (Signe Hasso). Unbeknownst to him, she had fallen in love with the image of Saint George, and is greatly disturbed by the uncanny resemblance to their guest. Vidocq and Vernet steal and hide the jewels, intending to return for them later.
However, when the minister fires Richet (Gene Lockhart), his chief of police, for not recovering the jewels, Vidocq devises a much grander scheme. Through "deduction", he leads the minister to the hiding place of the jewels, and wins for himself Richet's old job. In that capacity, he gets Vernet's relatives hired at the Bank of Paris, which he intends to rob.
A complication arises when he bumps into Loretta, who turns out to have married her beau, Richet. After learning his new identity, Loretta blackmails Vidocq into resuming their relationship. Vidocq tells Vernet to go ahead with the robbery that night. That day, he goes out walking with Therese and her younger sister Mimi. When they are alone, Therese informs him that she has figured out that he stole the jewels. However, she does not care. She is quite willing to follow him, even if it means embarking on a life of crime. Meanwhile, a jealous Richet bursts in on his wife and threatens to kill himself. Instead, in a fit of anger brought on by her cold response, he shoots and kills her.
With that impediment out of the way, Vidocq informs the Vernet clan that he has changed his mind; he will hunt them down if they go through with the robbery. Nearly everyone is content with their new jobs - all that is except Emile. He ambushes his former friend, forcing Vidocq to kill him. Then he confesses to the minister. He is forgiven by all of the De Pierremonts and welcomed into the family.George Sanders as Eugène François Vidocq
Signe Hasso as Therese De Pierremont
Carole Landis as Loretta
Akim Tamiroff as Emile Vernet
Gene Lockhart as Chief of Police Richet
Alma Kruger as Marquise De Pierremont
Alan Napier as Houdon De Pierremont
Jo Ann Marlowe as Mimi De Pierremont
Vladimir Sokoloff as Uncle Hugo
Pedro de Cordoba as Priest
Leona Maricle as Owner of Dress Shop
Fritz Leiber as Painter
Skelton Knaggs as Cousin Pierre
Fred Nurney as Cousin Gabriel
Gisela Werbisek as Aunt Ernestine (as Gisella Werbiseck)
Marvin Davis as Little Louis
Sam Harris as Stage Show Spectator (uncredited)
Julius Tannen as Bank of Paris Manager (uncredited)