One day Moomintroll notices that something strange has happened in the Moomin Valley - everything is gray! Not just the sky and the river, but the trees, the ground, and the Moominhouse, too! Moomintroll runs to ask the well-read Muskrat if he knows what is happening. Muskrat declares that this is the way things tend to look like before the Earth faces an awful fate coming from the sky.