"It is Princess Harriet Hamsterbone to the rescue when Heady the hydra's egg is stolen, but her search leads her to a castle accessible only by a rat with a very long tail"--
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 Princess Harriet climbs an enormous beantalk, she finds an even bigger surprise--a giant rabbit is keeping a goose and a girl who is half-harp-half-hamster are prisoner, and it's up to Harriet to save the day"--