"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"--
The last member of a line of explorers, unfailingly optimistic Pigsticks hires a hapless delivery hamster named Harold to be his companion for a quest that wends through jungles, deserts, and mountains in search of the Ends of the Earth.