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.
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.