Daisy Wells and Hazel Wong are spending the Christmas holidays in snowy Cambridge. Hazel is looking forward to a calm vacation among the beautiful spires, cozy libraries, and inviting tea-rooms.

But there is danger lurking in the dark stairwells of ancient Maudlin College and two days before Christmas, there is a terrible accident. At least, it appears to be an accident—until the Detective Society looks a little closer, and realizes a murder has taken place. Faced with several irritating grown-ups and fierce competition from a rival agency, they must use all their cunning and courage if they’re going to find the killer before Christmas dinner.