Misty Valley is a valley on a branch line in the television series. It first appeared in the sixth season episode The Fogman. Cyril, a resident of the valley, was employed as a fogman until the Fat Controller acquired an electronic foghorn to warn the engines of landslides. The foghorn actually ended up creating one, derailing Thomas and almost destroying Toby after he nearly crashed into Thomas' train, but luckily Cyril had laid some detonators to warn Toby.
It later appeared in the eleventh season episode Thomas and the Storyteller. Thomas planned to take the storyteller to Misty Valley, which was mentioned to be the rumoured home to several magical creatures, but ended up having to take a detour to rescue Percy from a flooded river. Later, in the same season, Thomas is seen blowing his new whistle in the valley.