Ralph Bellamy as Ellery Queen

Margaret Lindsay as Nikki Porter

Charley Grapewin as Insp. Queen

Mona Barrie as Nurse Marian Tracy

Paul Hurst as Page

James Burke as Sgt. Velie

Leon Ames as John Stack

George Zucco as Dr. Edwin L. Jannery

Blanche Yurka as Mrs. Augusta Stack

Charlotte Wynters as Miss Fox

Tom Dugan as Lou Thomas

Olin Howland as Dr. Williams

Dennis Moore as Dr. Dunn

Jean Fenwick as Alice Stack

Pierre Watkin as Crothers

Byron Foulger as Hospital Orderly (uncredited)