Alicia Berenson, a painter, murders her husband of seven years, Gabriel Berenson. She neither denies her guilt nor provides an explanation for the murder. In fact, she is either unable or unwilling to speak at all. Detained at home prior before going to trial, she makes her only statement about the murder in the form of a painting, which she titles Alcestis, after an ancient Greek play.  

Among the fascinated crowds who visit the gallery to see the painting firsthand is Theo Faber, a professional psychotherapist and the primary narrator of the novel. He is both professionally and personally intrigued by Alicia’s ongoing silence. Theo’s interest in psychotherapy stems from his own struggles with mental health. Raised by an abusive father, Theo credits his former psychiatrist Ruth with helping him to recover from suicidal depression. As the story develops, Theo reveals more about his own personal life, including his relationship to his wife, Kathy, an American stage-actress whose buoyant personality gives Theo his first taste of real happiness. After finding suspicious messages on her laptop, however, he begins following Kathy hoping to catch her in an affair.  

At trial, Alicia is declared not guilty by means of diminished responsibility. Years later, Alicia has continued to maintain her silence despite the best efforts of the staff at The Grove, the psychiatric ward where Alicia has been institutionalized since the trial. Theo remains fascinated by Alicia, and he applies to work at The Grove to uncover the cause of her silence. At the Grove, Theo meets Diomedes, who runs the Psychiatry unit; Indira, a friendly therapist; Yuri, an easygoing nurse; Stephanie, the stern manager of the Grove; Rowena, an art therapist; and Christian, with whom Theo does not get along. Theo also meets the patients at The Grove, including Alicia, who has not responded to treatment and remains heavily medicated.  

Hoping to break through to Alicia, Theo feels that he must better understand her life in order to discover the source of her trauma. He requests interviews with those who knew Alicia before the murder, including Jean-Felix, whose gallery represented Alicia’s art. Theo also meets Alicia’s brother-in-law, Max Berenson, who claims that Alicia had been seeing a therapist unofficially at Gabriel’s insistence. During a visit to Alicia’s family home, Theo learns a good deal about Alicia’s unhappy childhood from her cousin, Paul, and her unpleasant aunt, Lydia.    

In Alicia’s diary entries, written prior to Gabriel’s murder, she reflects upon the death of her mother in a car accident that she feels was in fact a deliberate and suicidal act. She also writes about her passionate feelings of love for her husband and her hatred of Max, who has attempted to kiss and touch her inappropriately on several occasions. In the present day, Max calls in a complaint to The Grove regarding Theo’s behavior, and Diomedes agrees that Theo has transgressed professional boundaries. Despite orders to stop contacting Alicia’s friends and family, Theo meets again with Jean-Felix, who recommends that Theo read Alcestis by Euripides. In the play, a woman offers to sacrifice herself in place of her husband, who is all-too willing to accept her sacrifice.  

At The Grove, Theo has some breakthroughs with Alicia, who at first responds well to his attempts to engage her in art therapy before attacking him without warning. He is encouraged by this response, as it shows that she is in some way expressing her feelings, though Theo’s treatment of Alicia is abruptly cut short when she brutally attacks another patient. Before the hospital staff sedate her, she surprises Theo by giving him her diary. In it, he reads that Alicia was being stalked in the days before Gabriel’s murder.  

Theo’s personal life unravels as he follows Kathy and confirms that she is conducting an affair with another man. Spying on the man, Theo finds that he is married and that his wife is ignorant of the affair. Theo then returns to Alicia’s childhood home, where he has a breakthrough. Paul tells Theo that after the death of Alicia’s mother, her father wished aloud that Alicia had died instead. Theo realizes that, psychologically, her father killed her in that moment, and that something similar must have triggered a traumatic response in her on the night of the murder. At The Grove, he confronts Alicia with his discovery, and she finally begins to speak. She recounts the night of the murder, claiming that the man who had been stalking her tied her up and murdered Gabriel. Theo, however, believes that she is lying. The next morning, staff at The Grove find Alicia in a coma after a presumed drug overdose. Theo, however, accuses Christian of attempting to murder Alicia with an injection, and the police are summoned.  

Theo returns to the home of Kathy’s affair partner. He enters the home to confront the man’s wife, who is revealed to be Alicia Berenson. An unreliable narrator, Theo has been manipulating the timeline of the story to conceal his stalking of Alicia and his involvement in the death of Gabriel. In her final diary entry, hidden from Theo, Alicia explains what actually happened on that fateful night. Masked to hide his identity, Theo ties up both Alicia and Gabriel with rope. Hoping to expose Gabriel’s disloyalty, Theo offers Gabriel a choice: his life or Alicia’s. Gabriel chooses to save himself and Theo leaves without killing anyone. However, Gabriel’s willingness to sacrifice Alicia triggers her unresolved trauma regarding her father. She picks up the gun and shoots Gabriel several times, killing him. Years later, she recognizes Theo as her stalker when he begins working at The Grove. She decides to feign ignorance until she is sure about her identification and better understands Theo’s motives for coming to The Grove. When she finally agrees to speak with Theo, she lies about the events of Gabriel’s murder to indicate to him that she knows about his involvement. Theo, not Christian, gives Alicia an injection that renders her comatose to silence her and hide his complicity, though he insists that he had no idea that Alicia would kill Gabriel.  

Later, Theo and Kathy have left London and are unhappy in their marriage, rarely speaking, and Alicia remains in a coma with little chance of recovery. Chief Inspector Allen, the officer in charge of Alicia’s case, visits Theo at his home and reveals that he has found Alicia’s final diary entry, which exposes Theo’s crimes. As the inspector reads out the diary entry, Theo observes that it is snowing and catches a snowflake on his tongue.