Mainland's Decay {Sodor's Decay AU}
6 parts Complete [Literally just "Sodor's Decay" but it takes place on the mainland.]
Our protagonist is Class 40, now known as Andy, who spends his days working on the mainland, along with other diesel engines, and a few steam engines who, by law, can't be scrapped yet.
All of them unaware that the Decay is about to begin, and it all started with something that looked harmless; Rain.