Dr. Christine Allison is a woman who finds herself convicted of manslaughter after performing a mercy killing on her terminally ill, married lover. Having served two years in prison, she faces a difficult struggle to rebuild her life, as she is unable to find employment due to her criminal record. Her situation begins to improve unexpectedly when she is approached by Peter Finch, playing the role of Stephen Dane, the man who had previously prosecuted her. He offers her a unique opportunity to look after his wife, Diane Cilento, who is suffering from mental health issues. Initially suspicious, Christine questions Stephen's motives for seeking her help, suspecting that there is more to his request than meets the eye.
Stephen's reason for hiring Christine appears to be a need for a trained medical professional who does not hold the authority to commit his wife, Liane, to a mental asylum, unlike licensed doctors. With her medical license revoked, Christine is seen as an ideal candidate for the job, despite her reservations. Faced with limited options and driven by a sense of desperation, she agrees to undertake this delicate responsibility.
As Christine becomes more involved with the Danes, her unease about Stephen's true intentions deepens. Her suspicions grow stronger when Judith Furse as the first Wardress, and other characters, hint at underlying secrets. The situation escalates when Liane's father, Cyril Cusack as Captain Ferris, unexpectedly appears while the Danes are away. Christine had previously been told that Liane's mental instability was caused by her father's tragic death in a car accident, but he leaves without seeing his daughter, despite her pleas. This visit raises doubts about the authenticity of the story she was told.
Determined to uncover the truth, Christine confesses to Liane about her father's situation and convinces her to return to her childhood home in Ireland to reconnect with him. When they arrive, they find Captain Ferris drinking and living with a woman, revealing a disillusioned and troubled man. This encounter triggers another breakdown for Liane, who becomes increasingly fragile. During the chaos, Stephen arrives unexpectedly, and in her distress, Liane attempts to escape, falling and injuring herself. The injury turns out to be minor, but Christine, following her instructions, provides Liane with two pills from a bottle she possesses, intending to help her sleep and ease her agitation.
The following morning, tragedy strikes when Liane is found dead, and the bottle of pills is missing. An inquest is held to determine the cause of death, and the coroner J.G. Devlin uncovers details about Christine's turbulent past. She defends herself by accusing Stephen of orchestrating events to divert suspicion away from himself. During the proceedings, Christine notices Captain Ferris scrutinizing his heirloom pocket watch, even though Liane had stolen it the night she died. Ferris admits that Liane took the overdose herself; he discovered her dead and took the remaining medicine away.
It is revealed that Ferris had a history of blackmail and corruption. He had previously tried to bribe Stephen by sending his own young daughter to his hotel room when charges against Ferris were dropped—charges that Stephen claims were dismissed for reasons other than corruption. This led Ferris to begin blackmailing Stephen, and when Stephen refused to pay more, Ferris sought revenge. In a tense climax, Ferris is confronted by the police and, while leaning against a rotted fence, accidentally falls to his death.
In the aftermath, Stephen asks Christine for a ride, and together they drive away, leaving behind a web of deceit, blackmail, and tragedy. The story ends on a note of unresolved hope amid the dark shadows of the past, emphasizing themes of morality, corruption, and the complexity of human motives.
