The Missing Coach was an episode that was originally going to be part of the second season, but it was cancelled in the middle of filming and replaced by Thomas, Percy and the Coal.
Donald and Douglas (now 9 and 10 respectively) realise they only have numbers painted on their tenders, so no one would tell them apart if they swapped tenders. The inspector introduces them to Duck who shows them around and at night the twins put Gordon and Henry in their place when the two were teasing them about their whistles. One afternoon, Douglas is shunting in the yard and worries about being sent away, unfortunately forgetting to shunt Thomas' Special Coach. The twins decide to swap tenders so as to convince the Fat Controller that Donald has taken his goods train, but he is not fooled and reprimands Douglas severely.
- This episode was based on the story of the same name from the Railway Series book, The Twin Engines.
- In an interview with David Mitton released on SiF shortly before his death in 2008, he confirmed that the episode was in production and half way through filming when Britt Allcroft decided that it would be too difficult for young children to understand, so the crew filmed Thomas, Percy and the Coal instead. It is assumed that Donald and Douglas swapping tenders to fool the Fat Controller is what would have made the plot hard to comprehend for young children. David also mentioned that he was in possession of all the original footage filmed for this episode.
- Six screenshots are all that is currently publicly visible of the filmed footage: a scene of Douglas shunting the coach can be seen in the 1989 annual, a close up of Douglas is seen in various books, posters, and on Douglas' Take-Along card (it is also seen on the cover to the New Zealand rerelease of The Deputation and other Stories on VHS), various stills of the twins confronting Gordon and Henry at the sheds can be seen in a Japanese book and other merchandise, another confirms Duck as a character, one shows an image of one of the Scottish twins beneath the coal hopper with Duck by his side, and the final shows a portion of the opening. Recently Britt Allcroft's nephew stated that she also had the original footage.
- This is the first episode known to have been cancelled. However, the first season episode, Down the Mine, was originally planned to be the series pilot, but was re-shot and pushed back to much later in the season.