Mavis was arrogant until being brought down to earth after her embarrassing incident at the Ffarquhar crossing. Despite this, Mavis is reliable, honest, hard-working engine, and unusually for a diesel, shows respect for the steam engines. However, unlike most engines, hauling trucks makes her feel important.
She is a BR Class 04 with added cowcatchers and side plates. These versions were built for the Wisbech and Upwell Tramway.
- Thomas and Oliver (cameo)