When Bronwyn gives her father Gareth Griffiths a sausage sandwich for his lunch, she has no idea the lengths Nipper the dog will go to for a bite!

It's a big day in Pontypandy, Gareth is opening the Pontypandy mountain railway line and station; he has refurbished the old engine, The Pontypandy Flyer, to take people up and down the mountain. But the water tower threatens to fall and put the train in danger.