A new tank engine named Arthur has a spotless record, meaning he has never been naughty or had an accident. Thomas gets a cheeky idea and plays a trick on Arthur to spoil his spotless record.

Donald and Douglas like Castle Loch, as it reminds them of their old home in Scotland. They are instructed to take a special load for its special reopening. Douglas teases Percy about a possible monster, and he and Donald get into an argument. Disaster strikes when a fallen tree and landslide leave them stranded all night, leaving the twins to worry about the monster.