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.

While continuing to help his classmates solve their problems, Humphrey, pet hamster of Longfellow School's Room 26, faces many surprises, like rolling in a hamster ball, a substitute janitor who might be an alien, and the possibility of Mrs. Brisbane retiring.

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.

When the school fair features a best class spirit contest, the students of Mrs. Brisbane's class prepare a tribute to Humphrey and Og, who are disappointed when hot weather threatens to prevent the class pets from attending.

"The students in Room 26 are throwing a birthday party, and Humphrey is surprised when he finds out who it's for!"--

"To Humphrey and the students at Longfellow School, spring seems impossibly late this year. Fortunately, planning a school Family Fun Night keeps the students (and classroom pets) busy as they look for signs of the changing seasons"--

Humphrey, the pet hamster of Longfellow School's Room 26, learns that his classroom is full of secrets, the most important of which is that a student will be leaving soon.

During a creative writing unit in Mrs. Brisbane's class, the students practice using their imagination with their very own writing journals--and Humphrey finds out that writing from his imagination is harder than it looks.

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.