Sharing your home with an unwanted guest can be murder. Elderly Mrs. Rampage lives alone in a large London house full of the antiques and heirlooms she's collected over the years. But she's struggling to cope, and as her only daughter lives thousands of miles away, she is persuaded to advertise for a housekeeper and companion. Reluctantly, she accepts the courteous and capable Mrs. Roach into No 5 to help her. With few possessions of her own, Mrs. Roach is in desperate need of a place to stay, but she soon has her own ideas about how things should be run in the house. And as Mrs. Rampage grows increasingly protective of her knick-knacks, and pushes at the boundaries of her new companion's personal privacy, the pair's initially amicable relationship soon turns sour. Before long, both women are thoroughly miserable, but stuck in unhappy coexistence with nowhere else to go. When Mrs. Roach digs in and makes it her duty to stay, the lives of both women become entangled in catastrophic circumstances.