Air date: December 3rd, 1986
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", despite that they don't mean any harm.
- Dark Is Not Evil: BoCo. It did seem that a diesel would stir up trouble much like Diesel in previous episodes, but BoCo had mistakenly took the trucks and didn't know it was Bill and Ben's.
- Eye Pop: Averted. The narration mentions that BoCo's eyes nearly pop out despite that 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.
- Sibling Rivalry: Bill and Ben shows shades of this when they argue about who is responsible for spreading the "diseasel" with their "coughs and sneezles".
- Sdrawkcab Name: Sort of. BoCo is named after the Co-Bo wheel arrangement, but Rev. W. Awdry though the two syllables reversed sounded better as a name.
- 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.