Set in the 1930s. At the opening, an elderly countess (Maggie Smith), her chauffeur and her maid, Mary, leave their home in the rain to travel to a country house where a variety of members of the English gentry arrive for a house/shooting party. Among the guests are a film star, an American producer and several others, including a valet (Ryan Philippe) who is not what he seems. The host of the party, Lord William Stockbridge, is an unpopular and unpleasant man, holding the purse strings of his family and wife in a bitter marriage. Over the weekend he pulls out of an investment scheme and threatens to cut off the countess' allowance, and one night at dinner it is revealed that he is sleeping with the housemaid Elsie. The guests retreat to the parlour to pretend nothing is wrong, but are forced to face reality when Lord Stockbridge is murdered in his study. The police are sent for; a bumbling detective (Stephen Fry) and his sharper subordinate. Though they get nowhere, the countess' maid, Mary, is poking around on her own and ultimately it is she who comes to the correct conclusion.