When heart-broken Sarah Quinn is left to care for her father and siblings when her mother dies, it’s hard to watch their loving dad, Fred, drift into drink and despair. With money tight, Sarah is determined to keep the family together. But they receive a shock when Fred Quinn announces he is to marry Mavis Swindel, the landlady of a boarding house on the edge of the moors. Mavis seems to offer the answer to the family’s problems, and soon they are all moving into her shabby lodgings. It quickly becomes clear that their stepmother has plans for her new family, and slowly but surely, Mavis takes over their lives. As her father becomes a stranger to his children, Sarah becomes convinced that Mavis has something to hide. But as her doubts turn into an obsession, does Sarah risk destroying everything she loves in her search for the truth?