Danny Dingle, Super Genius Inventor, has returned, and this time – it's serious! After an awful parents' evening, Danny and Percy's friendship is on the rocks. Thanks to Mr. Hammond spilling the beans about their couscous-projecting particle accelerator, they've been grounded until they're twenty-one! And what's more, they've got to compete against each other in the school's first ever parent-child sports day. Surely things can't get any worse ... can they?