From Dav Pilkey, creator of Captain Underpants, and acclaimed artist Dan Santat, a thrilling friendship adventure with all-new full-color illustrations and mini-comics throughout!Having a big best friend isn't always big fun...Ricky Ricotta loves his Mighty Robot. They do everything together, but it's sometimes hard for a small mouse to have such a big buddy! If only the Mighty Robot could find someone his own size to play with, Ricky might finally have some fun by himself.Little does Ricky know, his wish is about to come true. Evil Uncle Unicorn has a top-secret plan to trap the Mighty Robot so that he can take over Earth, and he's got a giant surprise in store. Once again, it's up to Ricky to save the planet -- and his best friend!