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- “Can't you see I'm busy! All I remember is he had a broken light and I couldn't understand a word he said!”
- ―Cranky recalling the yellow engine
Blue Mountain Mystery is a magazine story illustrated using images from the CGI television series. It was later published in the 2013 Holiday Annual and it was republished under the name Little Green Mystery and Engine Overboard!.
Thomas is very pleased because he is to help shunt trucks at the Blue Mountain Quarry. When he arrives, he sees a green engine that he had never seen before dart out of a tunnel. Thomas asks his narrow gauge friends about the little green engine. All of the engines make silly suggestions or pretend they are busy. Thomas is now very suspicious.
Thomas keeps seeing the mysterious little green engine, but he always races away. Finally, Thomas catches him and the little engine tells him that his name is Luke. The other little engines had been protecting him because he had done a very bad thing and Luke fears that, if his secret is uncovered, he will be sent away from Sodor for good. Luke explains that he arrived on Sodor by boat with a yellow engine. When they arrived, Luke wanted to be lifted out first and, as he was being lifted, he knocked into the yellow engine. The yellow engine then plummeted into the sea. Luke goes on to tell Thomas that when the engine was lifted from the sea, he was rusty and ruined. The yellow engine was then never seen again.
Thomas decides to go looking for the yellow engine. He puffs all over the island, but does not find anything. He then decides to ask Cranky at Brendam Docks as he would have been the crane who had lifted the two engines. At the Docks, Cranky is as cranky as ever. He tells Thomas that all he remembers is that the yellow engine had a broken lamp and he could not understand a word he had said. Thomas beams; he knows who the engine was.
Thomas races to the Sodor Steamworks where he asks Victor if he was the yellow engine. Victor admits that he was and that he was painted red after the incident. Thomas races back to the Blue Mountain Quarry where he tells Luke that he has found the yellow engine and he is healthy and happy.
Luke thanks Thomas for solving the mystery and the two engines become best friends. Best of all, Luke never has to hide again.
- Rheneas (speaks in speech bubble only)
- Sir Handel (speaks in speech bubble only)
- Rusty (speaks in speech bubble only)
- Skarloey (cameo)
- This story is based on the 2012 special of the same name.
- After reading the story, readers are given the chance of winning a copy of the Blue Mountain Mystery DVD by answering the question: "What colour was Victor when he first came to Sodor?"
- After the story, readers can colour in Luke.