Salty the diesel engine has a secret and all the other engines on Sodor want to know what it is. Join Thomas and Mavis as they meet Salty and discover the secret that Bill and Ben are still trying to figure out.
Diesel is the only one who can come in to help while Henry is being repaired. The trucks hear him bragging about how he'll replace the steam engines, and challenge him to prove his strength to cause another accident.
One of Edward's Halloween stories makes Percy afraid to go to the "haunted" smelters that night, and Thomas teases him about it. Duck is angry and decides to work with Percy to make him think he's surrounded by ghosts.
Thomas jokes about Jack Frost, a creature James scoffs but Percy fears in confusion. When they go to deliver coal, Percy gives his to the last station and is snowed over, so, passing, James mistakes him for Jack Frost and is horrified.
Gordon ignores a 'go slow' sign after he is accidentally switched onto an old branch line. As a result, he ends up taking a violent tumble off the rusty old tracks and comes to rest in a farmer's field.
Gordon brags that he's the fastest engine, but gets a surprise when Thomas' cargo, a jet engine, is activated as it's loaded and causes him to shoot down the railway at higher speed than anything either has seen.
Gordon claims that Edward is useless because of his age. Edward is sent to help Stepney, but Duck can't deal with Edward's freight-cars. He and Gordon, from behind, are stuck on Gordon's least-favorite hill, needing Edward.
Skarloey and Rheneas' line is closed down because of how much time Rusty spends repairing it. When the three are told they need to stay away from the quarry they're working at for safety for two weeks, Rusty tries to fix the line.
Percy discovers some wobbly rails, but no-one will listen to him. When Thomas is sent along the track, he runs into trouble and Percy comes to his rescue. Sir Topham Hatt promises to listen to Percy more in the future.
Skarloey grows afraid of an old wooden bridge when he almost falls off it. Later, Rheneas breaks down on the bridge and Skarloey is the only engine available to help. Can he overcome his fear to help his friend?
Henry feels ill, but Thomas and Percy don't believe him and leave a long line of trucks for him to haul. The trucks become too much for poor Henry and he soon breaks down completely and Emily has to come to his rescue.
Toby always loves looking at the island's windmill, but one day he is so distracted he crashes with some flour into a sail and is determined to help his friend not to lose his business, especially when lightning ruins it more.
Donald and Douglas jump at the chance to visit Lord Callum's castle to set up for a reopening-party since they're homesick, but become nervous that a monster is in the loch they become stranded near after a landslide hits the break-van.
Salty warns the others that a storm is on the way, but Thomas and Percy start teasing Salty by mimicking him. Salty's feelings are hurt and is glad when he has to leave the docks to collect Fergus. But during his journey, the storm arrives and danger follows...
Arthur and Thomas are disappointed when Thomas is chosen to run the new harbor-line since Thomas hates fish but Arthur loves the harbor. A track set wrong that causes Thomas to separate from the freight-trucks and sink may help them both.
Duncan is being impatient and tells the other engines to do their jobs faster. He completes his jobs before the others and is told to pickup an elephant statue. His carelessness sends him and the elephant out of control.
Diesel is needed to help Thomas and Fergus, and when he causes trouble Fergus tries to instruct him. Diesel lies that Fergus is ordered to work at the smelter's, but he is afraid enough of it to run away.
Sir Topham Hatt is cross with Skarloey for being late and worries that he will not be on time for the grand opening of a new station. But Skarloey's lateness gets Sir Topham Hatt and his wife out of a sticky situation.
Gordon wants to take the Duke and Dutchess around Sodor, but their private engine Spencer does, and is determined to show off how good he is. He ignores Gordon's advice to stop for water and Gordon has to help him.