Winter 1952, Monkswell Manor Guest House, near London.
The radio announces that a woman has been found strangled to death in London but Molly and Giles Ralston don’t have the time to reflect on this tragic event. They are about to welcome the first residents to their brand new hotel. A snowstorm is going to force them to share an enclosed space that is all the more oppressive because of their incompatible personalities.
 A policeman from the Berkshire police arrives out of the blue and announces that according to clues found at the scene of the crime, the killer who struck in the capital is likely to be joining them in their hotel. There is general disbelief at this news but…….
 Too late! « he » is already there. One of the residents has been assassinated. Everybody begins to suspect one another as they all seem to have a reason to have killed and a reason to kill again

Scene 1 – Late afternoon.
A woman has been murdered in London. A young couple, Mollie and Giles Ralston, have started a guest house in the converted Monkswell Manor. Their first four guests arrive: Christopher Wren, Mrs. Boyle, Major Metcalf and Miss Casewell. Mrs. Boyle complains about everything, and Giles offers to cancel her stay, but she refuses the offer. They become snowed in together and read in the newspaper of the murder. An additional traveller, Mr. Paravicini, arrives stranded after he ran his car into a snowdrift, but he makes his hosts uneasy.
Scene 2 – The following day after lunch.
The imposing Mrs Boyle complains to the other guests, first to Metcalf and then to Miss Casewell, who both try to get away from her. Wren comes into the room claiming to have fled Mrs. Boyle in the library. Shortly afterwards, the police call on the phone, creating great alarm amongst the guests. Mrs. Boyle suggests that Mollie check Wren's references. Detective Sergeant Trotter arrives on skis to inform the group that he believes a murderer is at large and on his way to the