Behind the Mask

Jack Holt

Jack Hart aka Quinn

Constance Cummings

Julie Arnold

Boris Karloff

Jim Henderson

Claude King

Arnold

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