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.
Percy is jealous and upset when Harold has to take his mail delivery because a signal is jammed, but Harold takes too much at once and crashes. Percy has to come to his rescue.
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.
Percy is very frightened when he passes an old mine at night and sees some buildings sink into the ground. He is even more scared when Donald and Douglas tell him about the "naughty gnomes".
None of the engines like to be in the middle of a train, so 'Arry and Bert enjoy putting steam engines in the middle. This causes trouble for Percy, but James is convinced that he can outsmart the diesels.
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.
Percy doesn't want to do dirty jobs and agrees to take a load of sugar to Mr. Jolly's Chocolate Factory. Unfortunately, Percy crashes right through the factory and ends up covered in chocolate.
Thomas is given the job of taking famous opera singer Allicia Botti to her concert, but she is not very impressed when she spies a mouse in Thomas' coaches.
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.
Skarloey and Rheneas' old line is closed down. Seeing how unhappy they are working at the quarry, Rusty is determined to restore the line to its former glory.
When a branch knocks away Peter Sam's whistle, Duncan teases him, and boasts that any proper engine has a whistle. To prove his point, Duncan starts whistling loudly, but it comes loose while he is delivering an organ.
