Phyllida Bright runs the farm on an estate lost among the green hills of Devonshire. But this is not an ordinary country house at all — the estate belongs to the husband of the famous Agatha Christie, Phyllida's longtime friend. At dinner, the hosts discuss with the guests the original methods of murder, but when Phyllida finds a corpse in the library the next morning, it comes as a surprise to her.… The housekeeper tries to help the police, but in vain, and she has to investigate the crime on her own. And after the second murder, there is no doubt: the killer is one of the guests!