Twelve-year-old Frankie Fish hates visiting his grandparents. Grandad Fish is cranky, and yells a lot, and has a creepy hook for a hand - plus he NEVER lets Frankie go inside his shed. But after a teensy tiny prank goes wrong at school, Frankie is packed off to Old-People Jail for the whole holidays. What Frankie doesn’t know is that Grandad has been building a home-made Time Machine in the Forbidden Shed, and the old man has big plans to get his missing hand back. But when Grandad goes back in time, he changes history and accidentally wipes out Frankie’s entire family - Nanna, Mum, Dad, even his annoying sister Saint Lou.

Somehow, everyone is gone but Frankie and Grandad! And it’s only a matter of time until Frankie disappears too…As the last Fish men standing, Frankie and Granddad must race back in time to undo this terrible mistake. But can they stand each other long enough to put the past back together again? And even if they manage the impossible - will Grandad’s wonky time-machine ever get them home?