Stella is the wife of Max Raphael, the deputy superintendent of a maximum security psychiatric hospital near London (based perhaps on Broadmoor, where the author's father was medical superintendent), and mother of a ten-year-old son. She becomes involved in an obsessive sexual affair with one of the institution's patients, Edgar Stark, a schizophrenic sculptor institutionalized after murdering and decapitating his wife.

Stark uses his affair with Stella to escape, and she runs away to London to join him. After a few passionate but squalid weeks in hiding, Edgar's illness resurfaces, evinced both in the violence he shows to a sculpture he's making of Stella's head, and in his paranoid jealousy. She runs away from him and is captured by the police and returned her to her husband, who has been fired because of his wife's role in the escape of so dangerous an inmate.

The family moves to a remote hospital in North Wales, where Max has a minor position, and Stella becomes severely depressed, to the extent that she stands by helplessly as her son dies in an accidental drowning. As a result, she is institutionalized--she returns to the hospital, not as the superintendent's wife, but as a patient. Edgar has meanwhile been recaptured (in North Wales, seeking out Stella either to take her with him or to kill her), but they never meet again, for Stella commits suicide.