Dunkin' Duncan is the twenty-fourth episode ever made in Season 6.
Rusty, Rheneas, and Skarloey go to the slate mines to help Duncan. Duncan is impatient and behaves rudely towards the others. While the others are taking some trucks back, Duncan pushes the trucks around and, while shunting some empties at the incline, gets his coupling tangled with a truck. The winch hauls the trucks and Duncan up the slope. Duncan's weight is too much for the winch and a coupling breaks, making Duncan run down the hill into the swamp. Duncan is pulled out and the Fat Controller makes him work at the mines as punishment until he learns to be "patient and careful".
- The narrator says "Rusty, Rheneas and Skarloey chugged cheerfully through the Sodor countryside", but Skarloey looks glum and Rusty is a Diesel.