The Plot Thickens

James Gleason Police Insp. Oscar Piper

Zasu Pitts Hildegarde Withers

Owen Davis Jr. Robert Wilkins

Louise Latimer Alice Stevens

Arthur Aylesworth Kendall

Paul Fix Joe

Richard Tucker John Carter

Barbara Barondess Marie

James Donlan Jim

Agnes Anderson Dagmar

Oscar Apfel Robbins

Alyce Ardell Josephine, Hildegarde's Maid (uncredited)

John T. Bambury Midget (uncredited)

Billy Dooley Gas Station Attendant (uncredited)

Frank Fanning Detective Fanning (uncredited)

Mary Gordon Woman with Bag (uncredited)

Reed Howes Museum Guard in Egyptian Room (uncredited)

John Indrisano Man in Line for Inspection (uncredited)

Lew Kelly Cassidy, a Policeman (uncredited)

John Miltern Mr. Gordon, Museum Guard (uncredited)