A. L. Kennedy 
Uncle Shawn and Bill and the Great Big Purple Underwater Underpants Adventure [PDF ebook] 

The fourth book in a hilarious, heart-warming series for children from Costa Award-winning author A.L. Kennedy, illustrated by celebrated cartoonist Gemma Correll.Hold onto your underpants – there’s a mysterious purple bottom explosion problem plaguing the world, and no one knows what to do! No one, that is, apart from Uncle Shawn. He knows he and his best friend, Badger Bill, can fix everything by visiting the Living Fish Tree at the bottom of the Pacific Ocean. As long as there is no dastardly villain with an army of evil clockwork clones on the loose, everything will be fine. And how likely is that…?