It is Christmas on the Island of Sodor. It is a busy time, but the engines love this time of year. All the engines that is, except for Duncan, the Scottish narrow gauge engine, who complains even more than usual.
During the day, Duncan complains to Rheneas about the cold weather. He then complains to Rusty about the apparent lack of sand. Later, he complains about the extra passengers slowing him down to Skarloey causing him to start losing his Christmas spirit.
By the time Skarloey returns to depot, he does not feel very festive at all. Neither do Rusty and Rheneas. Thomas arrives and tells them that even Duncan will be impressed by the brightly lit depot. Sure enough, he arrives and starts complaining. Thomas tells his narrow gauge friends that the Fat Controller is giving all of the standard gauge engines a new coat of paint. Duncan thinks this is unfair, but Rusty informs him that Mr. Percival is planning a similar treat for his narrow gauge engines. He is pleased, but then goes off moaning as usual. This gives Rusty and idea.
The next day, Duncan travels to the Steamworks for his fresh coat of paint where he finds the Thin Controller talking to Victor. Mr. Percival tells Duncan that he is upsetting the other engines with his constant complaining and that he will only get his coat of paint if he is cheerful for the rest of the day. He accepts the challenge and sets off to work.
On his way, Duncan meets Rheneas at a junction. Rheneas reminds him to go slow on the icy rails. He thanks Rheneas for the reminder. At Crovan's Gate, he has to wait while all the passengers climb aboard his coaches with their extra luggage. Skarloey arrives and notices that his attitude has completely changed since yesterday. Shortly, he gets held up at a frozen level crossing. To pass the time, the passengers start to hum a Christmas tune. He doesn't like the humming at all, but he grins and bears it.
Later, Duncan gets stuck behind Luke on a slippery hill. Try as he might, Luke can't reach the summit; his wheels will not grip the rails. Duncan is very impatient with him and upsets him. Unfortunately, Rusty is watching Duncan with interest. He realizes that he has upset Luke and decides to help him. As his sandbox is empty, Duncan drops some on the line himself. He then buffers up to Luke and gives him a push to the top of the hill. Rusty has seen everything. Duncan feels sad; he knows that he lost his temper and that means no new coat of paint for him.
The next morning, Duncan heads to the Steamworks anyway to apologize for his behavior. As Duncan begins to explain to Mr. Percival he is cut off mid-sentence. Mr. Percival explains that Duncan had done a very kind thing in helping Luke and such usefulness should be rewarded with a new coat of paint. Mr. Percival also says that he had been wrong to make Duncan be cheerful all day. Rusty goes on to say that he is just that sort of engine and, as Luke points out, it doesn't make him any less useful.