The mysterious Shadow Thief has been stealing from mice and shops in the mouse village and Gaston and Anatole are on the case. Little do they know that Paulette is his unwitting assistant.

The poor girl was conned by him into thinking that he was a spy and she accepts his job offer as his special spy assistant (a lookout) in order to make money to buy Doucette a very special birthday present. Complications occur when circumstances convince Pamplemousse that Anatole is the thief and is hunted by the authorities. Paulette redeems herself when she helps to ensnare the Shadow Thief at the cheese factory so that Anatole can bring him to justice and clears his own name.