Thomas & Friends: Sodor's Legend of the Lost Treasure

Thomas the Tank Engine wins a race against Bertie the Bus, who mentions that a new branch line is being built. This concerns Annie and Clarabel, who fear Thomas's branch line may be closed down. The next morning, Thomas plays a prank on Gordon the Big Engine which causes a derailment. As punishment for his misbehaviour, Sir Topham Hatt reassigns Thomas to assist in construction of the new branch line, while new tank engine Ryan is given Thomas's job while he’s away.

At the construction site, part of the ground subsides beneath the new track. Thomas misses the caution signs and falls into a cavern where he finds a pirate ship. He tries to tell Sir Topham Hatt about the ship, but Hatt thinks Thomas is making excuses. Rocky the crane is instead credited with discovering the ship, which is put on display at Arlesburgh Harbour.

Thomas meets Sailor John and his boat Skiff, the latter of whom has been fitted with wheels that allow him to travel on rails. John says he is looking for treasure but is hesitant to give Thomas details. The next day, Thomas neglects to tell Ryan about a faulty coal hopper, which leads to Ryan's wagons full of dynamite igniting. Thomas saves Ryan and disposes of the dynamite, but Hatt is furious with him, thinking that he was chasing Ryan with the dynamite. Hatt punishes Thomas by confining him to his shed for the rest of the afternoon.

Marion the steam shovel finds a treasure chest full of gold and jewellery, which Hatt keeps in his office overnight intending to donate it to a museum. Thomas meets a furious John, who demands the treasure be handed over. Thomas says Hatt has the treasure and refuses to help John take it. That night, John breaks into Hatt's office and steals the treasure, using Skiff and the pirate ship as his getaway. Thomas chases them through a junction where the minimum-gauge engines slow the ship by derailing their open wagons. A loose rope is caught on Ryan, who derails the flatbed carrying the ship, leaving John with only Skiff and the treasure.

At Arlesburgh Harbour, Thomas tries derailing Skiff to no avail. At the rail-boat launch ramp, John rows Skiff out to sea, and Thomas ends up partially submerged. Skiff knocks John and the treasure overboard. The treasure sinks to the bottom of the harbour, and John is arrested by the police. Thomas is rescued and attempts to apologise to Hatt, fearing he will be furious with him. Instead, Hatt is proud of Thomas as Ryan had explained everything to him, and Hatt assures Thomas that he will always be his "number one engine".

When the branch line is completed, Sir Topham Hatt gives a fully-repaired Thomas his old branch line job back, and lets him cut the ribbon to the new branch line, which he entrusts to Daisy the Diesel Railcar. The treasure is recovered and, now free of Sailor John, Skiff gives rail-boat tours of Arlesburgh Harbour.

• Keith Wickham as Salty, Bert, Sir Topham Hatt, Bertie, and additional roles
• Eddie Redmayne as Ryan^[4]
• Jamie Campbell Bower as Skiff
• John Hurt as Sailor John
• Steven Kynman as Duck
• Joe Mills as Donald, Douglas, Oliver, and Toad
• Olivia Colman as Marion
• Tim Whitnall as Mike and Oliver the Excavator
• Teresa Gallagher as Daisy, Annie, Clarabel, and some children
• Tom Stourton as Rex
• Jonathan Broadbent as Bill and Ben
• Nathan Clarke as Alfie
• David Bedella as Victor