The Snow Engine! is a magazine story.
Stephen and Bridget are very excited to see that it has been snowing as they look through the window of their grandparents' house. They decide to wrap up warm and rush out to build a snowman. Stephen and Bridget have hardly started building their snowman when the Fat Controller calls out to tell them he is going to the main station. Stephen and Bridget love seeing their engine friends and go with him. The Fat Controller tells them that they can build another snowman in the station yard.
A little later, Stephen and Bridget are building a snowman in the station yard when Percy puffs close. Percy asks what the messy mound of snow is supposed to be. Bridget tells him it's a snowman, but they haven't finished it yet. Percy tells them that a snow engine would look better and this gives Bridget an idea as Percy leaves to deliver some trucks.
While Percy has gone, Stephen and Bridget try to build a snow engine over and over again, but it is a lot harder than they had anticipated. They particularly struggle with the tall funnel which keeps falling down. Stephen tries to rebuilt the funnel, but he only causes the snow to topple down onto Bridget who is collecting snow underneath. Bridget thinks Stephen did it on purpose and tosses a snowball at him. Stephen decides to throw one back at his sister, but Bridget dodges it. The snowball hits Percy who is returning from his job. Percy puffs past the engine shed and whistles to tell the others he is approaching. The loud whistling causes the snow on the roof of the shed to fall off and right onto Percy. The little engine almost completely disappears beneath a white blanket of cold snow. Percy is startled, but unhurt. The children are very pleased; now they know what a snow engine looks like and they can use poor Percy as a model.
- Percy's lampirons and brake pipe are painted white when they should be black.