Air date: January 11, 2021 (UK), September 1, 2020 (US)
After being given a chance to prove himself by the Fat Controller, Sonny does not think his chances are good when he is shown hostility by Gordon and James. It seems Diesel is the only one really willing to be his friend, but it turns out Diesel is just tricking Sonny into doing his jobs for him, which Sonny finds out while pulling fish trucks. Diesel tries to follow after him, but gets diverted into a siding, derails and is about to fall into a pit. Sonny reverses to the siding, derailing the fish trucks over the points in the process, and saves Diesel. Although he had derailed the fish trucks, Sonny's heroic actions earn him praise from the Fat Controller as a really useful engine indeed.
This episode contains examples of:
- Break-Up/Make-Up Scenario: Sonny runs away in disbelief when he overhears Diesel telling Percy that he only pretended to be his friend to trick him into doing the jobs he doesn't like for him. When Diesel tries to follow him, he derails and hangs precariously over a trench. Sonny hears Diesel's cry for help and wastes no time getting him back on the rails despite their falling-out.
- A Day in the Limelight: Sonny's first and only starring role.
- False Friend: Diesel pretended to be Sonny's friend just so he can do the jobs for him.
- I'm Standing Right Here: Diesel tells Percy that he tricked Sonny into doing his jobs for him, but then realizes that Sonny heard everything.
- Jerk with a Heart of Gold: Diesel. Despite tricking Sonny to do his jobs, he made up for it by admitting to the Fat Controller that he was at fault for tricking him which made the Fat Controller commend Sonny for rescuing him.
- Reformed, but Rejected: Some engines (Gordon and James particularly) distrust Sonny for being a thief. After rescuing Diesel, the two commended him for his deed, though Gordon was rather half-hearted about it.
- Ungrateful Bastard: When Sonny pushed James from being splashed by watermelons, James didn't thank him and thought he was nothing but trouble. He apologized for misjudging him, however.
