The Missing Coach was an episode originally being developed for the second series but was cancelled and replaced by Thomas, Percy and The Coal. It was to be based on the story of the same name from The Railway Series book, The Twin Engines.
Donald and Douglas, now numbered 9 and 10 respectively, realise that they only have numbers painted on their tenders, the only ways to distinguish between them. The Fat Controller introduces the twins to Duck, who shows them around. At night, the twins put Gordon and Henry in their places after the two big engines tease them about their whistles. Shortly afterwards, Douglas is shunting in the yard and frets about being sent away, causing him to forget to shunt Thomas' special coach. The twins decide to swap tenders so as to fool the Fat Controller that they have nothing to do with the missing coach, but he is not fooled and severely reprimands Douglas.
- In an interview released on SiF shortly before his death in 2008, David Mitton confirmed that the episode was in production in 1985 and half way through filming when Britt Allcroft considered the episode unworthy of airing since she believed the plot would be too confusing for kids. It is assumed that the twins swapping tenders is what would have been too difficult for children to understand. To prevent the series from being an episode short, the crew filmed Thomas, Percy and the Coal to replace it. Mitton also mentioned that he was in possession of all the footage filmed for this episode.
- In said interview, David Mitton described the episode's plot as complicated without too much action.
- Six screenshots are all that is currently publicly visible of the filmed footage:
- A scene of Douglas shunting the special coach is seen in the 1989 annual.
- A close up of Douglas from the beginning of the story is seen in various books, posters, and on Douglas' Take-Along card (it is also seen on the cover to the New Zealand re-release of The Deputation and Other Stories on VHS).
- Various stills of the twins confronting Gordon and Henry at Tidmouth Sheds can be seen in a Japanese book and other merchandise.
- There is an image of one of the Scottish twins beneath the coal hopper with Duck by his side, and a final picture shows a portion of what would've been the opening.
- Britt Allcroft's nephew stated that she also had possession of the original footage.
- This is the first episode known to have been cancelled. However, the series pilot was never broadcast, but was re-shot as the twenty-fifth episode of the first series.
- Clearly, this episode was intended to air between Better Late Than Never and Break Van making it the fifteenth episode of the second series. Therefore, the episode Cows would have aired as the series premiere.
- The first two clips in the episode Break Van were originally filmed for this episode beforehand.
- This episode would have been the first appearance of Thomas' special coach in the television series, as well as the first episode to feature engines swapping tenders. However, Gordon and Henry swap tenders in the tenth series episode It's Good to be Gordon.