On a freezing winter's night, with the household in mourning following the death of the dowager Lady Croft, the residents of Thorncroft House are roused from their beds by the arrival of 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; she offers Lady Stanton and her servants all the hospitality at her disposal, however secretive and arrogant the new guest might be.

But tensions arise over the following days, with both visitors and servants trapped indoors by the snow, and Lady Stanton proving a difficult and demanding guest. The situation worsens on the discovery of the body of a young housemaid lying crumpled 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? Has her arrival anything to do with the housemaid's death? As the household remains trapped and tensions escalate, Harriet and her husband Matthew are forced to face the fact that they may be harbouring a murderer in their midst ...