When Mandy reads Moose Roberts' book about his mountain climbing adventures, she decides that she wants to be a mountain climber when she grows up – and climb the highest mountain in the world!

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.

When the Pontypandy Pioneers go to the fire station to complete their fire safety badge, Norman wants to prove to his cousin Derek that he can drive a fire engine.