Raffles, a clever, suave safecracker known as the amateur cracksman, has successfully eluded Scotland Yard for months, but after falling in love with Lady Gwen, he decides to go straight. When his close friend Bunny comes to his flat and attempts suicide in desperation over a large gambling debt, though, Raffles reluctantly decides to go through with a final robbery to save him. Gathering at the country house of Lady Melrose, who is fascinated by the handsome Raffles, he decides to steal her fabulous diamond necklace and hatches an elaborate plan to take the necklace while the house’s burglar alarm is disabled. The plan is put in jeopardy when Scotland Yard Inspector McKenzie arrives at the house after learning that burglars are planning to rob Lady Melrose. Using this information to his advantage, Raffles changes his plans and takes the necklace from the burglar Cranshaw, then returns to London. Cranshaw is subsequently arrested and informs the police that Raffles is the infamous cracksman and has the necklace. McKenzie hatches a plan to allow Cranshaw to escape so that the police can follow him to Raffles’ flat. Gwen overhears the plan and immediately returns to London to warn Raffles. The inspector follows Cranshaw, but Raffles has meanwhile convinced the burglar to run away instead of waiting to be arrested again. When McKenzie arrives at Raffles’ flat, he accuses him of the burglary. In front of Gwen, Raffles readily admits to being the amateur cracksman, but when Lord Melrose arrives to retrieve his wife’s necklace, Raffles offers to return it in exchange for the reward Melrose is offering. Planning to use the reward to pay off Bunny’s debt, Raffles then escapes through a secret opening in a grandfather's clock. Donning McKenzie's distinctive coat and scarf, Raffles manages to elude the police guards surrounding his building. After his escape, Gwen, who loves Raffles more than ever, plans to meet him later in Paris.