For no special reason Moomin wakes up in the middle of winter and can't go back to sleep. This is quite unheard-of. He is unable to wake the others, and finally, shivering, he makes his way outside into the bleak, unfamiliar whiteness. He meets Little My, who has woken up even before him, and Too-tick who lives in the bath-house. He meets the invisible mice, who also stays there for winter, and he almost meets the Lady of the Cold, the most fearsome of all winter`s manifestations... (thetvdb.com)