Drummond's wedding with Phyllis is interrupted when the inspector guarding their gifts is killed. He tries to trace the killers and uncovers the mystery of diamond counterfeiters.

John Barrymore
as Colonel Neilson

John Howard
as Captain Hugh 'Bulldog' Drummond

Louise Campbell
as Phyllis Clavering

Reginald Denny
as Algy Longworth

E. E. Clive
as Tenny

Porter Hall
as Dr. Botulian

Elizabeth Patterson
as Aunt Blanche

Nydia Westman
as Gwen Longworth

Halliwell Hobbes
as Prof. Bernard Goodman

Matthew Boulton
as Sir Raymond Blantyre