Molly is a powerful, bright yellow steam engine. She is proud of her strength and is happy to put it to use as one of Sodor's bigger engines. She often works pulling empty trucks to the coaling plant. Because she is a sensitive engine, she often worries about fading into the background. Sometimes taking "empties" makes her feel less important and sad, but in the end, she will usually see that taking "empties" is a vital part of operations and an important task after all. Molly has a peacekeeper attitude, tends to be rather sensible, and is looked upon as a "big sister" by some of the other engines. However, she is a sensitive soul, who can be easily embarrassed and can get upset by conflict, and will steam away to avoid it, but will usually have the courage to do what she thinks is right. Molly likes to be as good as everyone else and wants the other engines to think the best of her.
- Jinty's Twin Trouble (cameo)