Millie is Sir Robert Norramby's private French narrow gauge engine. She works on the Estate Railway.
Millie is a bubbly French engine who is owned by Sir Robert Norramby, who runs the narrow gauge line at Ulfstead Castle, where she lives and works. Her duties include assisting the groundskeeper and taking visitors on tours of the estate. For this, she has her own open-topped carriages. While the Earl was travelling the world, Millie stayed in her shed at the castle.
Millie once swapped jobs with Luke. Although she struggled to adjust to start with, she ended up loving the Blue Mountain Quarry, although she was pleased to return to her own job at the castle and even more pleased to have made friends with Luke.
While she was helping with construction of the Dinosaur Park, she was teased by Samson and Harvey for being afraid of the Megalosaurus model. She decided to pay them back by asking the groundskeeper to make a bonfire by the model volcano to create the illusion that it was actually active.
In Season 20, she was the referee for a race between Stephen and Glynn.
Millie is a narrow gauge engine. She has worked on the Earl of Sodor’s Estate Railway for many years. She is very loyal to the Earl and her relationship is like that of a personal servant. They have fun together and are as close as many friends, but there is also a certain formality to their relationship. Millie is a youthful, fun-loving, friendly engine who is full of spirit, and can be fiery when crossed. But she is also fair-minded and never spiteful. That said, she will take it upon herself to teach an uppity engine a lesson, should she feel the need. She always wants to do the best by the Earl and will defer to his judgement in all things, but when it comes to other engines, she has a mind of her own.
Millie is based on 0-4-0 well tank No. 8069 "Tabamar", built in 1911 by Borsig, under contract from Decauville. Unlike her basis, Millie has a rear coal bunker. "Tabamar" is preserved at the Chemin de fer des Chanteraines in France. Millie has been regauged from 1 ft 11 5⁄8in to 2 ft 3in.
Millie is painted French blue with white lining, brass fittings, a golden running board, boiler bands and wheel spokes. Sir Robert Norramby's crest is painted on her cab sides and her name painted in white on the sides of her boiler.
- Millie has the same whistle sound as Lady.
- She is the first female narrow gauge engine in the series.
- Millie is incorrectly portrayed as an 0-4-2 saddle tank engine in Thomas Land US.
- Millie is the first French-speaking engine in the series.
- In the twentieth season, Millie gained a tail-lamp.