In an old country house, the celebrations for Adrian Bennett's fortieth birthday are going well. Everyone is enjoying themselves - the guests; the actors who are acting out a murder mystery to entertain them; and Milly, who is helping her mother cook all the food. But the weekend is ruined when a real crime takes place. The road to the house is closed because of bad weather, and the police can't get there. So Milly decides to find out for herself who did it.