Janitors Laurel and Hardy are cleaning the office of a detective agency. They answer a telephone call from an inventor who claims to have created a destructive bomb he calls "The Big Noise." They pose as detectives and move into the inventor's home, where they must contend with his eccentric behavior, his oddball widowed aunt who takes a fancy to Hardy, and his misbehaving nephew. The inventor's neighbors are crooks who are eager to steal the new bomb.
Laurel and Hardy hide the bomb in a concertina and steal an airplane to bring it to Washington. However, the airplane is a remote control target used by the U.S. Army for gunnery training. Laurel and Hardy barely escape by parachuting to safety over the Pacific Ocean, and they dispose of the bomb by dropping it on a Japanese submarine.
- Stan Laurel as Stanley
- Oliver Hardy as Oliver
- Arthur Space as Alva P. Hartley
- Doris Merrick as Evelyn
- Esther Howard as Aunt Sophie
- Robert Blake as Egbert Hartley
- Veda Ann Borg as Mayme Charlton
- Frank Fenton as Charlton
- James Bush as Hartman
- Philip Van Zandt as Dutchy Glassman
- Robert Dudley as Grandpa
- Edgar Dearing as Motorcycle Cop