Boat building father and son join the river patrol service and get caught-up in a spy ring.
| Actor | Role |
|---|---|
| TTom GambleNobby Clark | Nobby Clark |
 Edward RigbyJoe Clark | Joe Clark |
 Jean GillieNancy | Nancy |
 Michael WildingDick | Dick |
 Marion GerthMimi | Mimi |
 Mavis VilliersBlondi | Blondi |
 John SalewHenri | Henri |
| HHenry B. LonghurstAdmiral Drake | Admiral Drake |
 G.H. MulcasterAdmiral Reynolds | Admiral Reynolds |
 Dennis WyndhamCaptain Raleigh | Captain Raleigh |
 Ian McLeanFirst C.I.D. Man | First C.I.D. Man |
 Joan HicksonWoman Carried Ashore (uncredited) | Woman Carried Ashore (uncredited) |
 Jack RaineHotel Manager (uncredited) | Hotel Manager (uncredited) |