When summer arrives, Humphrey, the pet hamster of Longfellow School's room 26, is surprised and pleased to learn that he will be going to Camp Happy Hollow.
When Humphrey the hamster returns to Mrs. Brisbane's class after the winter break, a new class pet and some other surprises give him an opportunity to reflect on the meaning of friendship.
After learning about Sherlock Holmes, Humphrey the classroom hamster follows clues to try and discover why Mrs. Brisbane is gone and Mr. E., a fun but not very educational substitute, is taking her place in room 26 at Longfellow School.
Humphrey the hamster is puzzled when unfamiliar students fill Mrs. Brisbane's classroom at summer's end, but he soon learns that his friends from last year are fine and that the new class needs his special help.
