The Sleeping City (1950)

An intern is shot mysteriously on an East River pier adjoining Bellevue Hospital. The chief investigating detective views this as a difficult case, so with the cooperation of the Commissioner of Hospitals he assigns a detective who had been a medical corpsman, Fred Rowan of the Confidential Squad, to go undercover as intern "Fred Gilbert."

Rowan becomes involved with the attractive nurse Ann Sebastian (Coleen Gray), and also becomes friendly with the popular elevator operator, Pop Ware (Richard Taber).

Ware, who works part-time taking bets, seems initially to be a benign character. But it becomes apparent that Ware has been loaning money to the interns, including the slain intern and another intern, Rowan's roommate Steve Anderson (Alex Nicol), who is depressed and commits suicide.

Rowan deliberately loses money betting with Ware, and Ware says that Rowan can pay off his bet by stealing "white stuff" -- narcotics. Rowan plays along, encouraged by Ann Sebastian. He stops providing drugs to Ware. Ware tries to kill Rowan, and is shot in a shootout on the roof of the hospital.

Investigators find that the nurse was worked as a courier for Ware. The movie ends with Rowan, turning aside pleas from Ann, placing her under arrest.