Undercover alien

"Life is going well for Rex until the school's guinea pigs suddenly vanish from the pet show. As a dinosaur-turned-PE teacher, Rex immediately gets the blame. Determined to prove he hasn't eaten any beloved pets, Rex - along with his friends Sandra, Anish and Bigfoot - set out to solve the guinea pig mystery. First they have to face up to the shifty city mayor, Jimmy Prigg, and then Rex must go undercover on a daring intergalactic rescue mission."--Publisher.