"The Beast Must Die" is a British drama series based on a well-known literary novel. The main character is a woman named Francis Cairns. Her six-year-old son is killed in a hit-and-run accident, and the driver chooses to flee the scene. As the story unfolds, Francis learns that the police are planning to freeze the investigation. As a result, she takes it upon herself to find the killer and simultaneously prepares a plan for revenge. Determined to seek justice, Francis is willing to take down the perpetrator, whoever they may be.