The novel alternates between two timelines. In the present day, Frances Jellico, a terminally ill woman, lies in a prison hospital bed, visited by Victor Wylde, a former clergyman who wears a borrowed dog collar to gain entry. Frances has been incarcerated for twenty years. She drifts between moments of clarity and waves of memory. The bulk of the story unfolds in her recollections of the summer of 1969 at Lyntons, a decaying English neoclassical mansion.
Frances arrives at Lyntons shortly after her mother's death. Her mother had been bedridden for years, and Frances served as her sole caretaker. With no money and no ties, she accepts a commission from Mr. Liebermann, an American who purchased the estate, to survey the garden architecture, with special attention to a classical bridge. She hopes the bridge will prove to be Palladian, a prestigious classical style featuring a temple-like pavilion, which would constitute a significant discovery. Frances is a self-taught expert whose published article on Palladian bridges caught Liebermann's attention.
The house is a ruin, gutted during wartime requisition by American soldiers. Frances is given converted rooms in the attic. While ripping up a foul-smelling carpet, she chases a dropped earring through a gap in the floorboards and discovers a metal tube fixed beneath the floor: a small telescope that functions as a spyhole, or "judas hole," looking directly into the bathroom below. She peers through it and sees Peter Robertson, the man Liebermann has hired to assess the house's interior. She replaces the board but does not remove the device.
From her attic window, Frances has already glimpsed Cara Calace, a young woman standing on the estate's dry fountain and shouting in Italian at Peter. Frances gradually learns that Cara is not Italian but Anglo-Irish, that she and Peter are unmarried despite Cara wearing a ring, and that Peter remains legally married to his first wife. After a week of avoiding the couple, Cara invites Frances to dinner. Frances squeezes into her dead mother's evening dress, girdle, and brassiere, constrictive undergarments she wears as a link to her past. The evening is warm and disarming. She drinks too much and vomits, and Cara holds her hair and helps her to bed. The next morning, Cara leaves a note with aspirin, the first letter Frances has ever received from a friend.
Frances begins eating all meals with the couple and stops working on her report. Over picnics by the lake, Cara tells Frances her life story: her childhood at Killaspy, a half-burnt Anglo-Irish house in County Kilkenny; her escape to Dublin, where she posed as Italian; Peter's arrival at Killaspy as a prospective buyer; and their complicated courtship, impeded by Peter's existing marriage and Cara's engagement to a local farmer named Paddy Browne. Cara reveals she had a child she later lost. Frances is captivated, hungry for intimacy she has never known.
Meanwhile, Frances cannot stop using the judas hole. She watches Cara and Peter argue and reconcile on their bathroom floor, and watches Cara shave Peter's face with tender precision. Peter privately asks Frances to keep an eye on Cara, warning that she is "not everything she seems" (114) and prone to fabrication. Strange events unsettle Frances: a dead mouse on her windowsill, a pillow in her bath, a toilet flushing with no one there, and a pale face at an attic window when she returns from a trip to London. She cannot determine whether these are Cara's doing or her own unraveling mind.
Cara tells Frances that her baby, Finn, had no father, that she was a virgin when she conceived. Peter later explains that the father was Paddy and calls Cara a "fantasist" (173) who cannot admit the truth. Behind the orangery, Peter breaks open a door hidden under ivy labeled "The Museum," revealing a vast room filled with the Lynton family's possessions sealed since the war: furniture, paintings, Chinese vases, and a telescope set in a velvet case with one tube missing. Frances recognizes the missing piece as the judas hole spyglass and says nothing.
Peter has been selling Museum items. He and Cara furnish their rooms lavishly with the Lyntons' belongings and outfit Frances's attic with a proper bed. In a tender scene, Cara undresses Frances, removing the girdle and brassiere, and tells her she is beautiful: "It's 1969. You should be free" (185). Frances accepts the stolen goods, the fine dinners, the wine. She stops working on her report entirely.
Cara tells Frances that Finn drowned when a boat carrying them to Scotland sank. Peter later contradicts this: He took Cara and Finn to Rome, fulfilling her dream of Italy. They argued, and Peter went to a bar. When he returned, Cara had fallen asleep in the bath with Finn in her arms, and the baby had slipped under the water. The boat story, Peter explains, was adapted from Cara's mother's real memory of horses screaming during a house fire. After Finn's death, the couple made a pact: Neither would ever leave the other alone.
Victor, who serves as vicar at the nearby estate church, becomes Frances's only outside contact. A former medical student who entered the clergy as wartime penance, he warns Frances that Lyntons is not good for her and urges her to leave. Tensions among the three residents escalate. Cara attempts to drown during a midnight swim; Peter and Frances resuscitate her. Cara cruelly reveals that she and Peter have never consummated their relationship, then mocks Frances's body. A telegram arrives from Liebermann announcing his imminent visit. Nothing can be put back in time.
Sitting atop the grotto, Frances opens her robe and presses Peter's hand to her breast, declaring her love. Peter pulls away, saying she has "misunderstood" (293). Across the lake, Cara stands on the jetty, watching.
Frances packs her suitcases to leave. She stops at Peter and Cara's sitting room to say goodbye and finds it in disarray, with four pulped orange halves on a cutting board. Cara emerges from the bathroom in a wet green dress. Through the door, Frances glimpses blondish hair floating in pink-tinged bathwater. It is Peter. Cara locks the bathroom door and throws the key out the window. In the ensuing struggle, Cara ends up leaning backward over the windowsill, holding on by her fingertips. Their eyes meet; Cara's expression is calm. She releases her grip and falls.
Frances goes upstairs and looks through the judas hole one final time. Peter lies motionless in the bath, his wrists slashed with Frances's botanical sample knife, the only sharp blade in the house. Cara had dissolved Frances's Valium in orange juice and drugged him before cutting his wrists. Frances walks to Victor's church, where he finds her in the vestibule with blood on her hands.
At trial, the prosecution argues Frances committed a double murder staged to look like a double suicide. Key evidence includes the knife, the Valium found in Peter's stomach, and a stolen library book. Her estranged father, Luther Jellico, attends every day, the first time Frances has seen him in nearly thirty years. Frances does not contest the guilty verdicts, craving penance. Near the novel's end, she reveals what she has never told anyone: One evening, after her mother pinched her waist as she always did, Frances took the spare pillow from behind her mother's head and held it over her face until she stopped struggling.
In the final pages, the narrative shifts to third person. Victor, now elderly, stands in an overgrown churchyard as a young gravedigger prepares Frances's grave. Lyntons has been demolished. Victor presides over the burial alone with the gravedigger, fulfilling Frances's wish that the service need only include "you, me, and the gravedigger" (3).