Jace Tanna is having the best summer holidays of his life! He has been allowed to help out at the Mash-Up Championship - a thrilling series of races through the wild terrain of Rumblemore Island, where Jace lives. The Mash-Up racers are scrap metal cars, powered by renewable electricity which is sourced from the island's smouldering volcano, Mount Rumblemore. Jace is thrilled just to be allowed to tidy up for the teams - but then something even more amazing happens - Jace gets to join a team and prove what a brilliant machine-fixer he is. Lexie, the team's daring young navigator becomes Jace's friend and the pair have a great time, careering around the racecourse. But they suspect that not everyone on the island is playing fair - especially the celebrity racing driver, Deesol Dragg. And the new friends soon realise that there's even more at stake than winning the Championship - the future of the island itself.