Imprisoned at the French garrison on the Isle of St. Noir for putting to death a patient suffering from an incurable illness, Dr. Paul La Roche escapes to the mainland, where he meets Dr. Henry Fontaine, his boyhood friend, and Fontaine's beautiful sister, Yvonne. As Fontaine is going blind, La Roche performs several operations for him, attracting the attention of Dr. Renaud, in Algiers, who offers him a position. La Roche, practicing as Fontaine, reveals his love for Yvonne during an excursion to a Bedouin camp. Then, Lieutenant Destin, from the prison, arrives and threatens La Roche with exposure unless he surrenders the hand of Yvonne.

Just out of jail and vowing to go straight, former jewel thief Boston Blackie, undertakes the reformation of a pretty blonde who has stolen a necklace from a cabaret dancer. He learns that the jewel belongs to the mother of the blonde girl, and the blonde's philandering father gave it as a gift to the cabaret girl. Now, Blackie must find a way to return the necklace to the owner's safe without arousing the suspicions of the girl's family.