Blue Mountain Mystery is the 2012 special, and the sixth installment in the Thomas & Friends lineup of specials. It was released in on DVD on September 3rd, 2012 in the UK, and on DVD and Blu-Ray on September 12th.
When Thomas is sent to work at the Blue Mountain Quarry, he discovers that a narrow gauge engine he had never seen before is hiding in the tunnels. Upon discovering who the engine is and why he is hiding, Thomas is determined to get to the bottom of the mystery, but discovering the truth proves to be harder than he had thought.
It is a busy day up at the Blue Mountain Quarry, and the narrow gauge engines are busy hauling slate to and fro around the quarry. Paxton's trucks are loaded up by Owen, the incline traction engine, and after a small chat with Skarloey, he sets off with his train. However, Paxton is stopped when a keystone from Blondin Bridge falls beside his line, and the alarm is sounded. As he is coming down the upper terrace, Rheneas hears the siren, but does not slow down until it is too late. Rheneas manages to clear the bridge just before it collapses, but is unable to stop, thundering down the cliffs at high speeds and knocking into walls. When he reaches the quarry floor, Rheneas' paint is scratched up, but fortunately he is not hurt. The narrow gauge engines all laugh in relief, until they notice that Paxton has been buried by rubble from the bridge and is badly damaged.
Meanwhile, on the Ffarquhar Branch Line, Thomas is pulling Annie and Clarabel, when they notice a strange red car lurching around the bend. The Fat Controller introduces Thomas to Winston, his new track inspection vehicle, and tells him that Paxton has been badly damaged and has to be repaired. In the meantime, he wants Thomas to do his work at the Blue Mountain Quarry, while Toby takes care of his coaches. After delivering his passengers to the next station, Thomas eagerly rushes off to the Blue Mountain Quarry, where he is greeted by his narrow gauge friends. Thomas spends the rest of the day working at the Blue Mountain Quarry, then delivers his train of stone to Brendam Docks and goes back to Tidmouth Sheds to rest.
The next day, Thomas is shunting trucks of stone at the Quarry, when he notices an unfamiliar narrow gauge tank engine darting out of one tunnel and then whooshing into another. He asks Sir Handel about this, but Sir Handel tells him that he must have seen a runaway truck and rushes away. Thomas spots the green engine later on, this time pulling slate trucks. He asks Rheneas about the engine, but Rheneas says he does not know what he is talking about and leaves. When Thomas sees the engine yet again, he asks Rusty about it, who tells him that he may have seen a mountain goat. Thomas tries asking Merrick and Owen about the green engine, but neither of them seem to know what he is talking about.
Annoyed, Thomas goes over to Skarloey to ask him about the engine, when he runs into the very engine at a junction. The little engine freezes in fear, then darts away to run into another tunnel, only to be blocked by Rheneas. Rheneas apologizes to the engine, addressing him as Luke, then moves into a siding while Luke runs into the tunnel and hides. Now knowing what the engine's name is and having seen him up close, Thomas confronts Skarloey and asks him who Luke is and why the engines refuse to tell him about him. The narrow gauge engines decide that, since Thomas is their friend, they will tell him about Luke, and Skarloey explains to Thomas that Luke hides in the Blue Mountain Quarry because he fears that he will be sent away from Sodor, as he did something very bad, though he does not explain what it was that Luke had done.
That evening, Thomas takes his train of slate to the Docks. When he stops at a junction, he wonders why Luke is scared and what he could have done that would be bad enough to send him away from Sodor. When he returns to Tidmouth Sheds, he asks the other engines what the worst thing an engine were to do would be. Percy recalls the time he tried to sneak up on the coaches, but ran into a luggage trolley and was covered in sticky jam and the Fat Controller's new trousers. Henry tells Percy that it was only an accident and that what he did was far worse, mentioning the time he refused to come out of the tunnel out of vanity and was bricked up. Thomas remembers the time he was shunting trucks at the lead mine, when he passed a danger sign and fell down a mine, but even then, he was not sent away. James mentions the time Diesel lost the flatbeds of Jobi wood on the unfinished bridge, but even he stayed on Sodor. Eventually, the engines fall asleep.
The next morning, at the Blue Mountain Quarry, the rubble from Blondin Bridge is being cleaned up. Rheneas is moaning about his ruined paintwork to the other engines, who tease him about it. Just then, Thomas arrives, and tells the narrow gauge engines he is confident there is nothing Luke could do that would result in him being sent away. When Skarloey asks if Thomas spoke to the other engines about Luke, Thomas denies it, claiming he wants to be Luke's friend. Satisfied, Skarloey tells Thomas to get back to work and reverses, just as Rocky swings a large ball of rock on the line behind him. Thomas whistles in an alarming way and manages to stop Skarloey just in time, who is very grateful that he prevented a nasty accident.
Upon seeing this, Luke finally warms up to Thomas and comes out of the tunnel, introducing himself to him properly and apologizing for hiding from him. Thomas is more than happy to be his friend, and together, he and Luke begin working together around the Blue Mountain Quarry. The two enjoy their time together, when Winston suddenly jerks into the Quarry, carrying the Fat and Thin Controllers with him. Luke becomes frightened and darts into one of the tunnels before either controller notices him, and the Fat Controller tells Thomas that Paxton has been fixed and will return to the Quarry. When both controllers leave, Thomas coaxes Luke out of the tunnel and asks him why he is hiding. Luke tells him that he did something very bad, but Thomas is sure it is nothing compared to the countless mistakes he has made. Luke finally decides to tell Thomas, but tells him not to tell anyone else about it. With that, Luke begins his story.
Back when Luke worked on another land, he was sent to Sodor to work at the Blue Mountain Quarry. He was very excited to go to Sodor, as it was his dream to work there. During the voyage, Luke stayed on the ship with a yellow engine, who came from a faraway country and spoke a language he could not understand. When the ship reached Brendam Docks, the men wanted to lift the yellow engine off the ship first, but Luke begs for them to take him off first. The men agree, and Luke is prepared to be lifted off the ship...
Luke pauses ominously. Thomas asks what happens next, and a tearful Luke tells him that he bumped the yellow engine into the sea. As he was being lifted off the ship, he was swung right into the yellow engine, who rolled right off the deck. Luke was sent to the Steamworks to be mended, but all he could think about was the yellow engine. As he never saw the yellow engine again, and because he had been left in the sea for so long, Luke believes the yellow engine was scrapped as he was deemed beyond repair. Luke is afraid that the other engines might tell the Fat and Thin Controllers about him, and he will be sent away from Sodor forever. Unbeknownst to either Luke or Thomas, Paxton has returned to the Quarry and is eavesdropping on their conversation, when Skarloey arrives and orders him to get back to work. Luke runs away in fear, and Thomas asks Paxton what he was doing, to which the diesel sheepishly claims that he has come to do his job. Thomas asks Luke to come out to say goodbye, but Luke is too frightened to come out. Thomas tells Luke that he will come back to the Quarry and that he is his friend, before leaving the Quarry.
The next day, Thomas is still worried about Luke, and accidentally runs through a red signal at a junction. As Thomas backs into a siding, Toby arrives, and Thomas asks him to take care of Annie and Clarabel while he does something very important. Toby is more than happy to help out despite his busy schedule, and Thomas leaves his branch line. Thomas begins a search for the yellow engine, and looks at almost every place on the Island, but finds no trace of a yellow engine anywhere. When Thomas meets Edward at a junction, Edward suggests that he go to the Dieselworks to find one.
When Thomas arrives at the Dieselworks, he discovers that Paxton is telling Diesel all about Luke, much to his horror. Diesel believes that Luke should be sent away from Sodor, as he could push another engine into the sea. Thomas gasps in shock and leaves the Dieselworks, but Diesel sees him before he leaves and orders Paxton to follow him, who is now regretting telling him about Luke.
As Thomas leaves the Dieselworks, he decides to go to Brendam Docks. When he arrives, he asks Cranky about the yellow engine. Cranky is irritated and gives Thomas little help, only telling him that the engine's headlamp was broken and he could not understand anything he said. Before Thomas can ask Cranky anything else, Diesel and Paxton arrive at the Docks, and Diesel asks Cranky where the Fat Controller is. Cranky refuses to help Diesel, when Thomas suddenly gets an idea and leaves the Docks. As Thomas leaves, Paxton tries to apologize to Thomas for telling Diesel about Luke, but Thomas is too far away to listen.
Thomas rushes into the Steamworks, where Victor and Kevin are both working. Thomas asks Victor if he remembered fixing a rusty yellow engine who spoke a different language, when he discovers that, much to his shock, Victor is the yellow engine. Victor quietly tells Thomas that he has never spoken to anyone about this, and it happened a long time ago. With that, Victor tells Thomas about how he arrived to Sodor.
A long time ago, Victor was told that he was needed on the Island of Sodor. The journey from his country to Sodor was very long, and before they arrived on Sodor, they stopped at a neighboring land, where a green engine, Luke, was loaded onto the ship, and although the two spoke different languages, Victor could see that Luke was excited. During the trip to Sodor, the chains securing Victor to the ship snapped, causing him to roll around the ship. When the ship arrived at Brendam Docks, Victor tried to tell the men that he was in trouble, but nobody on the ship spoke his language. Luke was unloaded from the ship first, but he swayed around as he was being unloaded and bumped into Victor. This caused Victor to roll backwards, and he rolled right off the ship's deck and fell into the sea. Fortunately, Victor landed in a jetty, but because of the bad weather, he had to wait in the sea for a long time, and when he was finally lifted out, he was in a terrible mess.
Victor says that the experience was chilling, but what frightened him most of all was that nobody understood what he said. So, when he was brought to the Steamworks and needed to be repainted, Victor decided to learn English; his first word was "red", which was the color he chose to be for his new life on Sodor. Now knowing Victor's side of the story, Thomas concludes that the event was only an accident, and rushes back to the Blue Mountain Quarry to tell Luke about this, confusing Victor when he mentions Luke's name.
Thomas races along back to the Blue Mountain Quarry, when he notices Diesel and Paxton with the Fat Controller. Diesel tries to tell the Fat Controller about Luke, but the Fat Controller believes he is making things up and orders him to take Mavis to the Dieselworks, while also telling Paxton to go back to the Blue Mountain Quarry. Once when they leave, Thomas returns to the Blue Mountain Quarry, where he is greeted by Luke and the other narrow gauge engines. Thomas tries to tell them that he spoke to Victor, but before he can say anything else, Skarloey interrupts him. The narrow gauge engines believe that Thomas told Victor about Luke and broke his promise, and all of them are cross, even Luke. Just then, Diesel and Paxton arrive at the Quarry, and the narrow gauge engines retreat to the upper terraces of the quarry. Thomas tries to tell the narrow gauge engines to not listen to Diesel, but they refuse to listen to him. He calls out to Luke, who angrily shouts that he never wants to see him again.
Thomas is desperate to get to Luke and explain the situation to him, and asks Owen to pull him up the incline. Owen is hesitant at first, but eventually gives in and allows Thomas to ride up to the upper terrace. Once when Rocky lifts Thomas onto the platform, Owen hauls Thomas up the incline. Diesel calls out to Luke that there is nothing Thomas can do for him now, and orders Paxton to fetch the Fat Controller. However, when Thomas tells him to bring Victor to the Quarry instead, Paxton does not know what to do and leaves the Quarry. When he gets to the top, Thomas tries to get to Luke, but he is too big for the narrow gauge rails and crashes into a set of buffers, hanging dangerously over the edge of a cliff. When Luke sees this, he goes over to Thomas and couples up to him, pulling him away from the cliff and saving him. Both engines are relieved, but neither are out of danger yet. As Thomas is pushed onto the incline platform, he becomes too heavy for Owen to hold and is launched down the incline, with Luke being dragged along behind him. Owen manages to gain control of the platform, and brings it to a stop just as it hits the quarry floor. All of the narrow gauge engines and Thomas laugh in relief.
Suddenly, Winston rattles into the Quarry, with both controllers with him. The Fat Controller is infuriated that Thomas is causing trouble at the Quarry instead of running his branch line, and the Thin Controller orders Rocky to lift Thomas and Luke down from the platform. As Rocky lifts Luke up, Diesel tells the Fat Controller all about Luke, when Paxton arrives at the Quarry with Victor. Victor reassures Luke that he did not push him off the ship, and that it was only an accident. Luke is not convinced that Victor is the yellow engine, but when Victor begins speaking Spanish, Luke is finally happy for the first time in years. The Fat Controller congratulates Thomas, and the Thin Controller accepts Luke as an engine of his railway. However, the Fat Controller scolds Diesel for jumping to conclusions, and Diesel apologizes.
A few days later, Thomas arrives at the Steamworks. Luke and Victor are already there, and the former tells Thomas that he found a yellow engine. Rheneas then puffs out of the Steamworks, now painted in a new yellow livery. All four engines laugh.
- Sir Handel
- Peter Sam
- Sir Topham Hatt
- Mr. Percival
- Working Together - plays during the montage of Thomas working at the Blue Mountain Quarry, and again while he is working with Luke
- Blue Mountain Mystery - plays during the end credits
- Percy mentions the time he tried to sneak up on the coaches, but hit a luggage trolley and was covered in sticky jam and the Fat Controller's trousers, which he did back in A Scarf for Percy.
- Henry refers to the time he was too stubborn to come out of the tunnel and was walled up, which happened during the events of The Sad Story of Henry.
- Thomas recalls the time he went past a danger sign and fell down a mine to the other engines. He later tells Luke about this. This refers to Down the Mine.
- All of the aforementioned moments from these episodes were remade in full CGI by Nitrogen Studios for this special.
- James mentions the time Diesel lost the flatbeds of Jobi wood on the unfinished bridge, which happened during Misty Island Rescue.