Simon Mouse wants adventure-any kind of adventure. But he gets more than he had in mind when he falls out of the back end of a moving van. He finds a new family with a colony of mice who live above the snack shop of a flea market. But there are dangers as well as fun at the flea market. The mice have plenty of food, but must dodge cats, dogs and owls to get it. Through it all, he wonders if he will ever find his parents again.