My Gym Teacher Is an Alien Overlord - David Solomons - Bog

Zack and Lara have superpowers. Luke has new school shoes and a burning sense of resentment. He KNOWS that aliens disguised as gym teachers are about to attack Earth but will anyone listen? No. So one dodgy pact with a self-styled supervillain later, and Luke is ready to save the world. He just need to find his trainers.