Thomas & Friends: Day of the Diesels is a 2011 animated adventure film and feature-length special of the British television series Thomas & Friends. It is the first (and only) special to be a spin-off around a character from the series; so the star is Thomas' best friend Percy. The film is produced by HIT Entertainment and animated by Nitrogen Studios.

Plot

New engine, Belle extinguishes a fire, but runs out of water. Thomas and Percy take her to the Steamworks where Sir Topham Hatt congratulates her and says they need another fire engine. Belle suggests a road/rail hybrid fire engine she knows named Flynn and arrangements are made to bring him over from the Mainland. Thomas starts to spend more time with Belle and later Flynn when he arrives. Percy feels left out, as well as from everyone else, and is convinced by Diesel, to visit Diesel's friend: Diesel 10, at the rundown Dieselworks. Diesel 10 will be Percy's mentor and new best friend. Diesel 10 informs Percy that Sir Topham Hatt does not care about the state of the Dieselworks and Percy says he will ask Thomas.