Sidney Howard adapted E. W. Hornung's novel The Amateur Cracksman about a charming upper-class jewel thief who outsmarts Scotland Yard.
A. J. Raffles (Ronald Coleman) when stealing a diamond bracelet for Gwen (Kay Francis) leaves a note indicating it is his "farewell appearance." Gwen agrees to marry him, and he decides to start a new life. But he finds his friend Bunny in the bathroom with the gas on because of a 1,000 pound gambling debt he paid with a bad check. So after a game of cricket he plans to steal the necklace of his friend Lady Melrose. Police are guarding the residence; but Raffles overhears burglars outside, disconnects the alarm, opens a window, and then forces the burglar Crawshaw to give him the necklace after he has taken it from Lady Melrose using chloroform. This gentleman thief even lets the lower-case thief do his dirty work. When the police reset the alarm and close the window, Crawshaw sets off the alarm on his way out and is caught. Raffles tells Gwen of his problem and that he has done wrong again. Lord Melrose offers a thousand pounds as a reward to catch the thief.
The inspector lets Raffles go so that he can have him followed in London. Gwen confronts Raffles as she realizes he is a jewel thief; but she stays with him, hoping for better adventures than crime. The inspector arrives at Raffles' apartment looking for the escaped Crawshaw, expecting to be led to the real thief. Crawshaw with a gun demands the necklace from Raffles or he will kill him. Raffles portrays the judge sentencing him to be hanged and takes the gun away. Then he is tied up, and Crawshaw is caught; but the inspector arrests him as the amateur cracksman. Raffles tells Bunny where the necklace is so that he can have the reward, and Gwen returns the stolen bracelet he gave her. All seems to be settled, but then Raffles dashes out and escapes wearing the inspector's coat and hat.
This charming caper reflects an aristocratic view of a gentleman clever enough to get away with major crimes; but it is innocent in a way because no one really gets hurt.