Grandpa lives with his family in a beautiful seaside town called Sunnysands. Everyone thinks he spends all his time stuck in his armchair, but he has a magic shrinking cap which only his grandson, Jason, knows about. When Grandpa puts his cap on, he becomes small enough to fit into Jason's pocket, not to mention his toy plane and car. Grandpa is playful and mischievous but always a force for good. He turns up in all sorts of unlikely places and creates comic mayhem which Jason has to sort out. Together, Grandpa and Jason make a great team and have a host of hilarious adventures.