A grandmother has an adventure for the first time in her life when she decides to have a night out.

Geoffrey's relationship with his fiancée is threatened by Ameuset, a princess of Egypt awakened after five thousand years. Originally a six reel feature, only short fragments of The Dust of Egypt survive today.

Retired businessman F.G. Lawrence favors Philip Preston for a son-in-law; Mrs. Lawrence prefers Reggie, the Dainty Dude. There's trouble, right there. Mrs. L. becomes suspicious of a stout stranger prowling about the place and tells Mary, the husky cook, to point him out to Serena Slim, the slender sleuth. The mysterious fat man happens to be Mary's beau, so she sics Serena onto John Bouncer, Philip's fat uncle. Serena is some "shadow" and the police must be called in to stop the comedy of errors which follows. After explanations all around, Lucy nestles her pretty head on Philip's shoulder while her parents soothe Bouncer's ruffled feelings.

The story follows three men—C.O. Darlington, C.O. Drudge, and C.O. Dusenberry (whose shared initials give the film its title)—who deceive their wives by faking illnesses to go on a secret vacation together.