The Gang's All Here (1939)

John Forrest is anticipating a quiet retirement spent penning detective fiction when he learns that a priceless collection of jewels belonging to a foreign potentate, Prince Homouska, has just vanished from the safekeeping of the Stamford Assurance Company. Aided by his butler, his Cockney assistant and his (initially) unwilling wife, Forrest sets out on the trail of the thieves.