In a small English town, there is a general practitioner named Gemma Foster. She believes she has a wonderful life - a loving husband, a fulfilling profession, and an intelligent son. They lead the comfortable life of a middle-class family and want for nothing. However, one day Gemma begins to suspect her husband of infidelity, although initially she thought he had some other terrible secret. Her suspicions turn out to be true. Now, Gemma is determined to seek revenge on her soon-to-be ex-husband.