It's Christmas time and Shinobu sensei makes a Christmas party for her students. The cake was sponsored by the principal, however, a knife is found in it, having traces of blood on it. The blood belongs to a woman that was found dead in her flat. How is the knife in the cake linked to the dead woman? And what's with that weird UFO the kids were seeing? Also, the young inspector is trying hard to gain Shinobu's interest, but has to fight against his opponent.