- “That looks like a good place for an adventure!”
Duncan and the Old Mine is the twentieth episode of the ninth season.
Duncan is looking forward to taking holidaymakers to see the Culdee Caves when his job is given to Bertie instead. Mr. Percival wants him to deliver coal trucks to the Transfer Yards with Rusty as the machines at the coaling plant have broken down. On his way to the coal mine, Duncan sees an old line leading towards some bushes and ignoring Rusty's reminder that they have work to do, he goes down the old line which leads to an old mine entrance. Carelessly, Duncan crashes into a roof support, causing the entrance to collapse behind him. Duncan carries on into the mine until he hits something, which he thinks are buffers - until he hears a squeaking noise and realises that he ran into some coal trucks. Pushing the coal trucks, Duncan finds that the mine shaft was actually a mine tunnel when he arrives at a bordered-up exit and then he pushes the trucks out of the mine. Rusty, who had been looking for Duncan, finds him with the coal trucks, so they take them down to the Transfer Yards where Thomas & Mr. Percival are waiting. Duncan tells Mr. Percival about his adventure and Mr. Percival tells Duncan that he was very lucky and that he must think clearly when he wants to have another adventure.
- Mr. Percival
- Mighty Mac (cameo)
- Culdee (mentioned)
- Bertie (mentioned)
- Sir Topham Hatt (mentioned)
- Transfer Yards
- Rheneas Viaduct
- Middle Station
- Culdee Caves
- The Mountain Line
- The Coaling Plant (mentioned)
- Skarloey Coal Yard (mentioned)
- Going by production order, this is the twenty-first episode of the ninth season.
- The old coach from the seventh season episode, The Refreshment Lady's Tea Shop can be seen at the Transfer Yards.
- The way Rusty said "Look what you've done, Duncan" is different in the PBS Airing, Lost and Found and the US DVD release.
- Rusty was referred to as female in the first American narration on TV. However, on the US DVD release, Rusty was referred as male.
- Duncan and Rusty do not have drivers and Duncan also does not have a fireman.
- In the scene of the trucks approaching the boarded-up exit, after they stop a shadow moves across one side of the door.
- When Rusty and Duncan arrive at the Transfer Yards, the truck behind Rusty is derailed.
- Some wires can be seen on Duncan's cab when he pushes the trucks.
- When Duncan passes by the Middle Station by the beginning, a steam platform is visible beside the station.