Peter Sam is pulling some trucks, but when he has to stop to take on water, they use the opportunity to break away. The trucks are thrilled to be on their own - until they come to the ravine bridge and fall in. Peter Sam is told off and Duncan has great delight in teasing him. Rusty tries to stop this by telling the story of an engine who tried to cross the Old Iron Bridge but never made it to the other side due to loss of control. Duncan thinks this is a load of nonsense and puffs away, so the Driver and Fireman plan a trick to play on him for when they cross the bridge that night...