Duke loves taking the holidaymakers for trips into the mountains. Duke always travels up the steep slopes slowly so that the holidaymakers can admire the view. The other engines tease Duke by calling him "Granpuff" or "Slowcoach", but Duke does not mind.
One sunny morning, Duke is taking some passengers to the lake. Since the tourists are only visiting Sodor for a day, Duke is determined to make their day a very special. Duke soon reaches the lake and puffs slowly to allow his passengers to look at the water and the boat. The lake is Duke's favourite place. Duke then reaches the picnic area and his passengers leave the carriages. Duke tells the passengers to enjoy their lunch, but not to miss their train or they will miss their boat back to the mainland.
That afternoon, Duke collects his passengers to take them back to the harbour, but soon Duke begins to feel short of steam. Duke has to stop so that the driver can clean out his tubes. Stuart bustles up and teases Duke, but Duke's driver tells Stuart that he must help get Duke's passengers to the harbour. Stuart gets ready to give Duke a push.
Soon, Stuart and Duke reach a hill. When they get to the top, Stuart goes to the front of the train to pull Duke who has now started to feel better and decides to play a trick on Stuart. Duke starts to puff as noisily as he can, sending the sound echoing around the hills.
When Stuart and Duke reach the station at the harbour, the people on the platform start to cheer. One of the men thinks that Duke has had to push Stuart down the hill. Stuart is very cross. Duke pulls up next to Stuart and thanks him for helping his passenger to catch their boat. Stuart realises that this is what is most important and feels silly for getting so cross.
- Duke has two green coaches in the second illustration, but has four blue ones throughout the rest of the story.