On a freezing winter's night, the residents of Thorncroft House are roused from their beds by an unexpected visitor. Although Lady Stanton seems reluctant to explain the reasons for her visit, housekeeper Harriet Rowsley would never turn a stranger from the door. But tensions arise, with both visitors and servants trapped indoors by the snow. The situation worsens on the discovery of the body of a housemaid lying at the foot of the stairs. A tragic accident. . .or something more sinister? Who exactly is Lady Stanton, and why has she come to Thorncroft? As the household remains trapped, Harriet and her husband Matthew are forced to face the fact that they may be harbouring a murderer in their midst. . .