"That's not fair!!!"
Life is not fair! Horrid Henry feels that the rest of the world is against him and he wages a constant war against the adults. Like any headstrong young boy, he is determined, relentless, he doesn't hold back and he never admits defeat! He will stop at nothing to outwit the enemy and teachers, relatives and babysitters avoid him at all costs.
Henry is chosen as one of the entries for the Brainbox of the Year competition, Peter stays with Great-Aunt Greta, while Mum and Dad go on a Great Escape out of Ashton.
When Mum goes out of the house, Henry takes advantage of his babysitter Mad Martin's obliviousness and watches the Gross Class Zero marathon. However, when the show comes to life within Henry and Peter's eyes, they are now on a mission with the Gross Class Zero crew to defeat the Evil Emperor - Darius Drek, and his children; Drusilla Drek and Damian Drek, and save the universe before it's too late.