After Thomas (John Hasler in UK, Joseph May in US) wins a quick race against Gordon (Keith Wickham in UK, Kerry Shale in US) and reaches the end of the line at Vicarstown Station, he is introduced to Gordon's brother, The Flying Scotsman (Rufus Jones), who is taking part in The Great Railway Show on the Mainland, encouraging Thomas to try and take part as well.
Though every engine on Sodor wants to take part, Sir Topham Hatt (Keith Wickham) has not made up his mind yet, and Thomas fears he won't be picked to go to the competition. After getting an idea to be streamlined for the competition, he passes his idea on to Sir Topham Hatt, who believes it to be a perfect idea for Gordon, much to Thomas' dismay.
At Brendam Docks, Thomas has a run-in with several of the competitors for The Great Railway Show (Teresa Gallagher, David Bedella & Rob Rackstraw) when their rail ferry docks there by mistake, and as a result, one of them is left behind. The engine, a beautifully-painted one from India named Ashima (Tina Desai), makes a bad first impression on Thomas, but upon getting another idea regarding her paintwork from Annie and Clarabel (Teresa Gallagher), he heads to the Steamworks to be repainted, but is forced to reveal his new idea to Sir Topham Hatt, who selects James (Keith Wickham in UK, Rob Rackstraw in US) and Emily (Teresa Gallagher in UK, Jules de Jongh in US) to be repainted instead. Running into Ashima again after learning she took Annie and Clarabel down his branch line, Thomas is convinced by her to just be himself and take part in the shunting challenge at The Great Railway Show since he is so good at shunting.
However, thanks to a trick by Diesel (Kerry Shale) involving Den (Keith Wickham), Dart (Steven Kynman), and Paxton (Steven Kynman), Thomas suffers an accident with Norman (Keith Wickham) at Knapford Junction, and has to be left behind to have his front end mended while Percy (Nigel Pilkington in UK, Christopher Ragland in US) takes his place. In the end, Thomas is able to go, despite not being fully repaired, when it is discovered that Gordon left without his safety valve being properly installed while he was being streamlined, leaving his boiler vulnerable to overheating, especially at high speeds.
At The Great Railway Show, Henry (Keith Wickham in UK, Kerry Shale in US) loses the strength competition, James and Emily lose the Best Decorated Engine award to Ashima's fellow engine from India, Rajiv, and due to not waiting to have his safety valve installed, Gordon's boiler explodes, forcing him to drop out of the Great Race. Thomas takes Percy's place in the shunting competition, but sacrifices his chances to win when he sees Ashima's track blocked by a derailed flatbed and switches tracks with her so he hits the flatbed instead. However, the judges decide to award Thomas the win alongside Ashima for his excellent sportsmanship. Sir Topham Hatt and the other Sodor engines are very proud of Thomas.
With The Great Railway Show over, Thomas invites Ashima to come back to Sodor to catch her ferry home to India there, allowing her to spend some more time with her new friends.
As for Diesel, he finds himself on-board a ship leaving Sodor after getting one of the crates from his trick stuck on him.
- Team Griffin/Eeveelution, The Griffin Family, Vinny Griffin, Glenn Quagmire, Cleveland Brown, Joe Swanson, Mitzi, No Feet, Tutu, Doug Funnie, Skeeter Valentine, Roger Smith, Bender Bending Rodríguez, Minerva Mink, Wubbzy, Widget, Walden, and Daizy guest star in this film.