Diesel 10 is a renegade diesel engine on the Island of Sodor who is 10 out of 10 for brutal strength and devious deeds, and is out to destroy the harmony of Sir Topham Hatt's Railway.

When we last saw Diesel 10, he had fallen into a barge sailing down a Sodor canal. Although no one knows his whereabouts, we can only guess he's up to no good.