While conducting research on the physical impact of crime, Dr Clitterhouse decides to become a criminal himself. After a few jewelry thefts, the doctor meets Jo Keller, a major figure in the criminal underworld. He takes a liking to Keller and becomes a member of her gang, supplanting "Rocks" Valentine. Once he has enough data, Clitterhouse tries to return to his normal life, but Valentine finds out his identity and blackmails him.