Mavis is a diesel that belongs to the Ffarquhar Quarry Company on Thomas' Branch, She is one of younger diesels there. She currently works on the branch taking stone trains up the track or out on the mainline.
Mavis was built by Drewry Car Co in 1961 with added cowcatchers and was bought by The Ffarquhar Quarry Company in 1962 to take stone up and down the line until she had an incident at a level crossing the manager told her that she was forbidden to leave the Quarry. Later Mavis told the trucks that when she took another load of stone The truck would bump her at the level crossing and tell no one she asked them, it suddenly backed fired when Toby was to take the train and The Trucks decided to bump him instead, Toby was left still on the track on the damaged bridge over the rushing stream Mavis was horrified of what she had done and pulled the trucks away and then with a great effort she started to Toby back on firm rails after that The Fat Controller was very pleased including the Manager of Mavis' Honesty and courage so as an reward she was allowed to do occasional trips around the branch and the mainline.
Mavis used to be arrogant but after her incident she had been brought back to earth and is now reliable, honest and a hard working engine. She also haves a deep respect for the steam engines on the island.