Air date: December 3rd, 1986
Adapted from: Main Line Engines, "The Diseasel"
Bill and Ben are tank engine twins who work at a china clay quarry. Their jobs are to take the china clay in trucks along the main line for engines and ships at the Harbour.
One day, Bill and Ben arrange some trucks and leave to pick up more, but return to their first loads gone. Their drivers find a patch of oil on the ground and realize a diesel is responsible for taking the trucks. Mishearing this as "diseasel", the twins argue who is responsible stating that "coughs and sneezles spread diseasels". Their drivers, laughing, stop the twins from arguing and make a plan to get the trucks back which involves removing the twins' nameplates and making them identical.
The twins find the trucks in a yard, with a large green diesel at the front. Ben hides behind, with Bill going forward to demand the trucks back. The diesel claims the trucks are his and tries to shoo Bill away, but when Bill disappears Ben rides forward surprising the diesel, thinking it's the same engine. This continues for a while, causing the diesel to get dizzy. The twins then reveal themselves to him.
Edward arrives at the scene and asks Bill and Ben what they're doing there. They explain that the "dieseasel" stole their trucks, but Edward scolds them for their rudeness. The twins apologize and the diesel forgives them. He introduces himself as BoCo and explains that he got his trucks mixed up with Bill and Ben's. Edward then sends the twins to pick up BoCo's trucks in exchange for theirs.
After the two leave, Edward tells BoCo that Bill and Ben don't mean any harm but can be maddening at times. BoCo laughs and replies that "maddening" is the word.
Tropes featured in the episode:
- Bratty Half Pints: Bill and Ben. Edward lampshades this by stating they're "maddening at times", but that they don't mean any harm.
- Dark Is Not Evil: BoCo. It does seem that a diesel would stir up trouble much like Diesel and Daisy in previous episodes, but BoCo mistakenly took the trucks and didn't know they were Bill and Ben's.
- Digital Destruction: In the restored version, a crew member's hands and the end of the set are visible when Bill and Ben leave their trucks of china clay at the docks and go to find more.
- Eye Pop: Averted. The narration mentions that BoCo's eyes nearly pop out even though they were spinning.
- Identical Twin ID Tag: Bill and Ben's nameplates, which the drivers had removed as a plan to get their china clay trucks back from the diesel.
- Malaproper: Bill and Ben misinterpret "diesel" as "diseasel", hence this episode's title.
- Sdrawkcab Name: Sort of. BoCo is named after the Co-Bo wheel arrangement
, but Wilbert Awdry thought the two syllables reversed sounded better as a name. - Sibling Rivalry: Bill and Ben show shades of this when they argue about who is responsible for spreading the "diseasel" with their "coughs and sneezles".
- Shout-Out: The line, "coughs and sneezles spread diseasels," is a reference to an advertising slogan first employed in the U.S. following the 1918 Spanish flu epidemic and later adopted by the British Ministry of Health during the Second World War.
- Team Dad: Edward serves this to Bill and Ben, scolding the twins for their behavior towards BoCo.
- Trickster Twins: Bill and Ben.
- Twin Switch: Bill and Ben pull this on BoCo.
