A classroom hamster has to be ready for anything, but suddenly there are LOTS-LOTS-LOTS of big surprises in Humphreys' world. Some are exciting, such as a new hamster ball. But some are scary, such as a run-in with a cat and a new janitor who might be from another planet. Even with all that's going on, Humphrey finds time to help his classmates with their problems. But will Mrs. Brisbane's unsqueakable surprise be too much for Humphrey to handle?