When a young pregnant woman named Rosie Jones boards a train, her enormous suitcase starts leaking blood. When later questioned by the police about the two dead bodies found inside, Rosie calmly reveals that they are her unfaithful husband and his mistress, resulting in her being sentenced by the judge to be imprisoned in a secure unit for the criminally insane for manslaughter on the grounds of diminished responsibility. Forty three years later, Walter Goodfellow, the vicar of the village of Little Wallop, is very busy writing the perfect sermon for a convention while completely oblivious to the problems in his house which include the unfulfilled emotional/sexual needs of his wife Gloria, who subsequently starts an affair with her golf instructor Lance ; the sexual desires and growing maturity of his teenage daughter Holly, who constantly finds new boyfriends; and his son Petey, who is frequently bullied at school. Eventually, everything changes with the arrival of a new housekeeper named Grace Hawkins. Grace becomes entrenched in the life of the family and begins to learn about the problems in the house: the neighbour, Mr. Brown's Jack Russell terrier Clarence, who consistently keeps Gloria awake at night by his constant annoying barking; the bullying of Petey and Gloria and Lance's affair. Grace commits to solving the problems in her own way by killing Clarence as well as Mr. Brown, sabotaging the brakes on the bullies' bicycles which injures one of them and killing Lance with a flat iron outside the house for videotaping Holly undressing one night. While Walter is preparing his sermon for the conference, Grace introduces him to humour and suggests adding it to his preaching method. Further, she discovers that he has let his relationship with his wife slide on account of his devotion to God and she teaches him that he can love his wife as well as God by drawing his attention to the erotic references in the Song of Solomon. As the problems in the household seem to gradually clear, Walter leaves for his convention. Grace’s actions are discovered when Gloria and Holly see her photograph on television in a news report showing her release and previous offences. It is then revealed that Grace is Gloria's long-lost mother Rosie Jones, explaining why she came to Little Wallop in the first place. After briefly processing the influx of information, Gloria argues and attempts to explain that when having a problem with someone, one cannot just kill them. Grace remarks that this is the one thing she and her doctors could never agree on. Despite their disagreements, Gloria tries to help Grace with Lance's body, but cannot handle it. Over a cup of tea, the three women decide not to tell Walter or Petey any of what has happened. When nagging congregant, Mrs. Parker comes over to discuss the problem of the "church flower arranging committee", Grace, under the false impression that Mrs. Parker is about to turn them in for their crimes, attempts to hit her over the head with a frying pan but is prevented by Gloria. Mrs. Parker, shocked by the attempt to murder her, has a heart attack and dies. Walter returns from the convention just then and sees Mrs. Parker's body, but doesn't realise that she is dead. Soon after this, Grace leaves the family when order is seemingly restored among the family. Walter then talks to Bob and Ted, the waterworks employees about the pond at the Vicar's house. They say that there is too much algae and the pond needs to be drained. Remembering that Grace has disposed of her victims in the pond, Gloria, with a disturbingly cheerful expression, offers the two men some tea. The film ends with an underwater shot depicting the bodies that had been placed in the pond, including the recently added bodies of Bob and Ted.
website Rotten Tomatoes reported that 56% of critics gave the film positive write-ups based on 87 reviews, with an average rating of 5.9/10. The site's critical consensus reads, "The stellar cast, including Kristin Scott Thomas and Dame Maggie Smith, is certainly an asset, but this blackcomedy is too uneven." On Metacritic, the film received an average score of 53 out of 100 based on 22 critics, indicating "mixed or average reviews". When the film was originally released in the United Kingdom, it opened on #4, behind Harry Potter and the Goblet of Fire and Flightplan. It regained the spot the next weekend.