Grandpa's childhood friend Granddad Gilbert comes to visit with his granddaughter Martha. Unfortunately, Gilbert has forgotten how to have fun so Grandpa sets out to remind him.
Mr Mentor the Inventor asks Dad to look after his Custard Puff Plopper, but the invention is not behaving itself! Grandpa is sure he can fix it - if only he can get inside.
Mr Mentor the Inventor has invented some Brillioso Bicycle Bells. Mr Liker Biker rushes to Dad's Bike Shop and starts trying them all out. How can Grandpa get him to leave Dad in peace?
When Mum leaves Jason and Grandpa in charge of her newly grown 'odd' vegetables who should arrive but Great Aunt Loretta? She wants to invent a stew for Mr Mentor but Grandpa is sure the vegetables don't want to be cooked.
When Floyd has a little accident in the garden, Grandpa suspects he is just pretending to be hurt. Grandpa wants to catch Floyd out - he just needs to find a way to make him run...
Jemima is looking forward to looking after a little boy called Shanay but when he arrives he's far too shy to play with anything. Will Grandpa and Jason together find a way to cure Shanay of his shyness?
Jason and Jemima are putting on a Captain Dumbletwit play. All is going well until Floyd turns up and takes over. Disaster strikes - but Grandpa is determined that the show must go on!
New girl at school Tiffany Jayne Grottington Pump comes round to play with Jemima. But Tiffany wants everything her own way. Grandpa puts on his shrinking cap and decides to teach her a lesson.
Bubbles the babysitter has a new kitten which she brings round to show to the Mason family. Unfortunately Floyd turns up and tries to make Bubbles jump. Before long Floyd gets a taste of his own medicine!
When Jason goes to the toyshop to choose a birthday present for his friend Dora, Grandpa can't resist shrinking and coming along too. But who should arrive in the shop? Dora's Aunt, the formidable Lady Prigsbottom!
Mr Liker Biker is looking after the Bike Shop when a very important customer turns up. Speedy Edie's shopping style sends Mr Liker Biker into a spin but Grandpa is sure he can help out!
Jason's cousin Max comes to visit Grandpa. Together they make a model caveman. When Mr Cave Man meets with an accident Grandpa has no choice but to step in and save the day.
Jason and Jemima go to Miss Smiley's Fun Kitchen club to learn how to cook some of her recipes. Floyd is also in the class and is soon up to mischief. Little does he know that Grandpa is keeping an eye on him!
Cousin Alvin has gone all sporty. He makes the Masons play lots of games and is desperate to beat them at everything, especially Table Football. Grandpa sets out to turn Alvin into a good loser.
The man in the beach hut opposite wants to be a real pirate. So when Horatio Heave Ho decides to dig up Sunnysands beach in search of treasure Grandpa comes to the rescue.
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Jason and Jemima go to Mr Whoops' toyshop to choose his Toy of the Week. But Floyd turns up and starts teasing Jemima who has picked up a cute little puppet. Grandpa rushes to Jemima's aid!
When Mr Whoops hurts his back picking up litter on the beach Grandpa decides that he needs a Litter Picker and who better to invent one than Mr Mentor. But a Litter Picker will need a bit of Grandpa's magic to work!
Mum is making everyone fancy dress costumes, but Great Aunt Loretta decides she needs some help. Mrs Maridadi the Dressmaker turns up and immediately has designs on Grandpa's Shrinking Cap.
Mr Whoops has bought a musical box for Miss Smiley and he's even made up a song to sing to her. But he keeps having little accidents with the musical box key. Good job Grandpa can shrink and get into tiny places!
Mum leaves Great Aunt Loretta in charge of her friend's goat, Mr Scoffbucket with disastrous results. When all Grandpa's plans to help fail he has to fly off to get help from a friend.
Bubble the babysitter has come round to teach everyone how to Flamenco dance because Miss Smiley is holding a "dancing tea!" But Great Aunt Loretta arrives and tries to take over.
Great Aunt Loretta has decided to make a clock for Mr Mentor's clock competition. Grandpa is keen that she should win because the prize is a holdiay! But her clock is a big disaster - until, that is, Grandpa steps in.
Mr Whoops wants a dog and Mum suggests that he tries looking after Wulfy for a day. Grandpa shrinks and goes to help out. But Wulfy ends up looking after Mr Whoops, instead of the other way round.
When a big cruise ship breaks down in Sunnysands, Mum invites the Captain to stay. He insists that they all perform various exhausting tasks every hour. But Grandpa has a brilliant plan to get rid of the bossy Captain.
Great Aunt Loretta is planning an invention with Mr Mentor and Grandpa decides to help.