A mouse is annoying the family of Mr. and Mrs. Evil J. Evil, the scientists, and Snagglepuss is offered food and lodging if he will get rid of the pest. The trouble is that the Evil's little boy has been experimenting with the mouse, and the furry rodent is now six feet tall!

Adapted from William Makepeace Thackeray’s book “Vanity Fair”, the film looks at the English class system during the Napoleonic Wars era.

Georgia Garrett is sent by jealous wife Elvira Kent on an ocean cruise to masquerade as herself while she secretly stays home to catch her husband cheating. Meanwhile equally suspicious husband Michael Kent has sent a private eye on the same cruise to catch his wife cheating. Love and confusion ensues along with plenty of musical numbers.