December 1864. As a cold winter wind scours the Worcestershire countryside, an excursion train comes through a tunnel in the Malvern Hills to be confronted by a blockage on the line ahead. The driver manages to slow the train down so that the impact is minimised, but the passengers are alarmed. The first person to alight is Cyril Hubbleday, the man in charge of the excursion to the delightful spa town of Great Malvern. He walks to the front of the locomotive and as he is talking to the driver, fireman and guard, Hubbleday is shot dead by a sniper.

Christmas is coming all too soon and Inspector Robert Colbeck and Sergeant Victor Leeming are under pressure to solve the case quickly. However, with a number of disputes and enemies in the shadows behind the seasonal excursion and the investigation hampered by heavy snow, the hunt for a cold-blooded killer is far from straightforward.