Catherine receives a book that reveals secrets from her past, linking her to the death of young Jonathan 20 years earlier. His father, Stephen, sent it to seek revenge after finding old photos of Catherine in his son's belongings.
Stephen sends a copy of the book to Catherine's son, Nicholas, and prints out explicit photos of her, sending them to her husband, Robert. A flashback reveals Jonathan's mother meeting Katherine, who blames her for denying any knowledge of him during the police investigation, even though Jonathan saved her son, Nicholas, from death.
Robert leaves home to read the book and refuses to communicate with Catherine. In a flashback, Jonathan spends a romantic night with Catherine in her hotel room, and days later, the police inform Stephen and his wife, Nancy, of the drowning death of their son in Italy.
In a flashback, Catherine is upset about Jonathan buying a ticket to London and demands an end to the relationship. While rescuing her son from the waves, Jonathan drowns, and Catherine sees him drowning but ignores everyone's warning. In fact, Robert insists on throwing Catherine out of the house.
Catherine reveals her past to her mother, who has dementia, and her colleagues reject her after the publication of "The Perfect Stranger." Stephen creates a fake Facebook page for Jonathan and contacts Nicholas, who has overdosed on drugs.
Nicholas is taken to the hospital after a drug overdose. Stephen attempts to kill him with a chemical injection, but Catherine intervenes and later confronts him at his home to reveal the truth.
Catherine reveals to Stephen that Jonathan raped her. Stephen relents, saves Nicholas, and tells him the truth. Robert apologizes, but she asks for a divorce. Eventually, Catherine reconciles with Nicholas and considers her future.