Ada Harris, a London charwoman in the 1950's, sees a Dior dress and decides that she's going to own one. First, she scrimps and saves her money, but when she has enough, and takes a trip to Paris, she learns that buying an original couture creation is a little harder than simply plunking down cash. Along the way to her goal, she manages to befriend a count, unite young lovers, and dodge customs.

When her doctor recommends that a widow pursue her unfulfilled life ambitions, he doesn't realize that she has always wanted to be a spy. Sending a letter to her congressman gets her an interview with the CIA and accidentally gets her an assignment to Morocco for a supposed easy task of picking up an encrypted code book. When the agency realizes their mistake, they send a super-agent to watch over her. Both are taken prisoner and the real agent is injured, leaving Mrs. Pollifax to use her considerable wits to help them escape and to save the day.