Ralph Bellamy as Ellery Queen

Margaret Lindsay as Nikki Porter

Charley Grapewin as Insp. Queen

James Burke as Sgt. Velle

Michael Whalen as Dr. James Rogers

Marsha Hunt as Barbara Braun

Fred Niblo as John Braun

Charles Lane as Dr. Prouty

Ann Shoemaker as Lydia Braun

Marion Martin as Cornelia

Douglas Fowley as Rocky Taylor

Morgan Wallace as Zachary

Byron Foulger as Amos

Katherine DeMille as Valerie Norris

Peter Bronte as Doctor's Assistant (uncredited)

Jack Cheatham as Desk Sergeant (uncredited)

Arthur Millett as Elevator Guard (uncredited)

Frank O'Connor as Ambulance Driver (uncredited)

Lee Phelps as Flynn (uncredited)

Jack Rice as Rogers' Assistant (uncredited)

Alan Ladd as Elevator Passenger (uncredited) (unconfirmed)