Thomas the Tank Engine & Friends Season 20 Episode 22 Three Steam Engines Gruff Episode Title:Three Steam Engines Gruff.Episode Description:One night, Percy is frightened by a strange sound from under the bridge at the Watermill. Toby is worried, though Thomas does not believe it to be true, until he too hears the sound. Toby and Percy believe it is a troll telling the story of how three goats had to cross a bridge with a troll under it. The trio become terrified of passing the bridge until it is revealed the sound was only coming from a cow stuck under the bridge.