Wilfred the Rat has found the perfect place to sleep for the night--a big stone building with all the comforts: dinosaur bones, stuffed elephants, and a cafeteria full of tasty sandwiches and pies. "Welcome to the museum!" say unofficial residents Prichett, Leo, Harry, and Buxton. But Mr. Thrawl, the museum director, has other ideas about uninvited guests...until he sees what they can do to earn their keep!