Because this winter has been particularly unusual, Moomintroll decides to stay awake and explore the season rather of hibernating as he would normally do to conserve energy. Winters, on the other hand, are quite different from what he had anticipated. The strangest creatures can be found wandering through the snowdrifts; the Moominvalley is enveloped in midwinter darkness; and, to top it all off, an eccentric visitor is about to arrive. Hemulen informs an astonished Moomintroll that this visitor will necessitate a number of precautions and will be known as Christmas.