Jack Holt
— Jack Hart aka Quinn
Constance Cummings
— Julie Arnold
Boris Karloff
— Jim Henderson
Claude King
— Arnold
Bertha Mann
— Nurse Edwards
Edward Van Sloan
— Dr. August Steiner / Dr. Alec Munsell / Mr. X
Willard Robertson
— Capt. E.J. Hawkes
Thomas E. Jackson
— Agent Burke
Martha Mattox
— Hotel Ansonia Maid
Jessie Arnold
— Eastland Hospital Nurse
Harry Tenbrook
— Man in Black / Henchman in Boat