When the diesels take over the Steamworks, Thomas and his friends must work together to win it back.
Day of the Diesels contains examples of:
- Big Bad: Diesel 10.
- Characterisation Marches On: It's rather odd these days seeing Paxton and Norman as willing troublemaking accomplices to Diesel 10, given later episodes establish them as ditzy but well behaved counterparts for their nastier bretheren.
- Continuity Nod: Steamies and diesels work together again.
- Covers Always Lie: Thomas is shown front and center on the boxart, despite the fact that Percy is the star of this film.
- Creative Closing Credits: As with the past two specials, the credits scroll over a montage of scenes from the movie as the titular song plays.
- A Day in the Limelight: In addition to Thomas, Percy has a big role here, and has more screentime and focus than the former.
- Distressed Dude: Thomas when Diesel 10 holds him hostage.
- Late-Arrival Spoiler: For those who were shocked upon seeing the sudden after-credits scene of Misty Island Rescue, that's where this movie starts. It even serves as a sequel to said film.
- Mood Whiplash: At first the movie starts off bright and pleasant, then comes a fire, and things get intense from there.
- Tears of Remorse: Percy gets these after seeing Flynn in his berth at Tidmouth Sheds.
- Wham Episode: The Sodor Dieselworks are restored, and Flynn and Belle join the Search & Rescue team.