One summer on the Island of Sodor, Spencer (voiced by UK: Matt Wilkinson/US: Glenn Wrage) arrives to help the Duke (voiced by UK: Matt Wilkinson/US: William Hope) and Duchess (voiced by UK: Teresa Gallagher/US: Jules de Jongh) with the construction of their new summer house. After being an absolute nuisance to all of the other engines by teasing and bossing them around, Thomas (voiced by UK: Ben Small/US: Martin Sherman) accepts Spencer's challenge to a contest of strength, taking heavy cargo around the island. Thomas's brakes fail after climbing a tall hill, and he runs out of control through an overgrown, abandoned line. There, Thomas finds an old abandoned Japanese engine named Hiro (voiced by Togo Igawa). Hiro doesn't want the Fat Controller (voiced by UK: Keith Wickham/US: Kerry Shale) to find out, fearing he will be scrapped, so Thomas promises to keep him his secret and work to make Hiro "Master of the Railway" once again. Later, he's taken to the Sodor Steamworks for repairs, where he finds old parts for Hiro. He takes them with permission from Victor (voiced by UK: Matt Wilkinson/US: David Bedella), the Steamworks engine, only to discover that Hiro's hiding place is dangerously close to the Duke and Duchess's new summer house.
The following day, Thomas tells Percy (voiced by UK: Keith Wickham/US: Martin Sherman) about Hiro, and asks him to do his own job while he helps Hiro. Percy misplaces his own mail trucks and breaks down while doing Thomas's job, so Thomas brings him to the Steamworks. The Fat Controller finds out about this and scolds Thomas by forcing him to do Percy's work. With nobody else to ask for help, Thomas tells the rest of his friends about Hiro. They all work together in bringing Hiro new parts, distracting Spencer, and keeping the operation a secret from the Fat Controller while Thomas and Percy try to find the missing mail trucks. Hiro makes friends with all of the engines, but gradually grows homesick. On the day that the last necessary part for Hiro is to be delivered, Spencer discovers Percy's mail trucks, only to be cornered by Thomas, James (voiced by UK: Keith Wickham/US: Kerry Shale) and Toby (voiced by UK: Ben Small/US: William Hope). The Fat Controller accuses Spencer of stealing the trucks and demands he return them to Percy.
While Thomas and Hiro wait for Percy with the last part, they hear Spencer's whistle and run. Spencer finds them and gives chase, but without the last part, Hiro falls apart and is forced to a stop. Spencer is suddenly distracted by Gordon (voiced by UK: Keith Wickham/US: Kerry Shale) while Thomas moves Hiro to a new hiding place. The Duke and Duchess are furious with Spencer for abandoning his own work, and Thomas asks to assist him, in order to keep his eye on Spencer and to gain the trust of the Fat Controller. Meanwhile, the other engines visit Hiro to keep his spirits up. When Thomas finally decides to tell the Fat Controller about Hiro, Spencer tries to stop him, but he is foiled by a rickety bridge which collapses beneath him.
When Thomas explains Hiro's situation to the Fat Controller, he reassures Thomas that he would never have scrapped the "Master of the Railway", and the following day, Thomas and Percy bring him to the Steamworks. There, Victor and his assistant, Kevin the Crane (voiced by UK: Matt Wilkinson/US: Kerry Shale), work together to restore Hiro. Once he's as good as new, Hiro with Rocky (voiced by UK: Matt Wilkinson/US: Glenn Wrage) rescues Spencer, and they work with Thomas on the summerhouse. Spencer apologizes to the two engines, saying they are "both fine engines and fine friends." Hiro misses his home island, so the Fat Controller arranges for Hiro to return home. A farewell party is held at the docks, and Thomas promises Hiro that Sodor will always be his home too.Martin Sherman as Thomas and PercyKerry Shale as Henry, Gordon, James, Kevin and Sir Topham HattWilliam Hope as Edward, Toby, The Duke of Boxford and RockyJules de Jongh as Emily, Mavis and The Duchess of BoxfordGlenn Wrage as SpencerDavid Bedella as VictorTogo Igawa as HiroMichael Brandon as NarratorBen Small as Thomas and TobyKeith Wickham as Edward, Henry, Gordon, James, Percy and The Fat ControllerTeresa Gallagher as Emily, Mavis and The Duchess of BoxfordMatt Wilkinson as Spencer, Victor, Rocky, Kevin, and The Duke of BoxfordTogo Igawa as HiroMichael Angelis as Narrator
A music video featuring an original pop rock song by Sam Blewitt singing "Go Go Thomas!", was released on the DVD.
A mobile app, entitled Thomas & Friends: Hero of the Rails, was developed by Callaway Digital Arts and released on 13 May 2011. Kirkus Reviews rated the app positively, commenting that it "delivers the same predictable experience they relish in video and book form, gently augmented with interactive enhancements."
A video game adaptation of the film was also released to the Nintendo Wii and the DS in the Europe on 29 June 2010. It was to be released in North America, but it has appeared to be cancelled indefinitely.
The movie was adapted into a Little Golden Book by the same name, which released on 11 May 2010.
DVD Talk gave a mixed review for Hero of the Rails, stating that it could be worth a rental while overall criticizing the film's plot, modernizations, and stating that it "[felt] like a poorly-thought-out extension of the series, designed simply to introduce a new format and score some cash." Commonsensemedia gave the film three stars, as they felt that it would not disappoint fans of the series but that it was also your "typical Thomas tale". About.com gave the movie four stars, opining that while the film looked better than they expected and praised the film for the value lessons it imparted, it was also "unremarkable compared to every other CG animated children's movie".