The setting for Iris Murdoch's novel is suburban London. One night, Lucas Gaffe, an eccentric and reclusive historian, tries to kill his stepbrother Clement with a baseball bat. This jealous Cain cannot forgive his sibling for stealing all their mother's love. A mysterious stranger intervenes and takes the blow intended for Clement. Although Lucas believes the intruder dead, this man, named Peter Mir, returns to life claiming to be a psychoanalyst with an interest in Buddhism. At first he wants retribution. Then, after a change of heart, he convinces the Graffe brothers to introduce him to their circle of friends.

This group includes Bellamy, a spiritual seeker who has given up most of his possessions and is corresponding with a Catholic priest about God; the widow Louise and her three adolescent daughters — the lovely Aleph, the scholarly Sefton, and the psychically gifted Moy; and Harvey, a student of modern languages who has been abandoned by his mother. These wayward souls are living unfocused and erratic lives; they are unable to take a stand for what they believe in or to lose themselves in love.

Peter Mir is the catalyst who spurs them to personal transformation. Louise puts it succinctly: "How this man has stirred us up. I think he's liberated us somehow. I feel liberated." Bellamy believes that Mir is an angel of mercy come to spread renewal. Others see this benefactor as the Green Knight, similar to the one who works wonders in a famous medieval tale. One thing is for sure, he brings a wildfire of change into the lives of all those he meets.

In her 25th novel, Iris Murdoch continues to demonstrate an ability to effortlessly interweave thought-provoking philosophical themes into her fiction. Here she infuses the story with a bit of mythology as well. The novel's impact stems from its serious treatment of a subject alluded to by Albert Schweitzer in his 1924 book Memoirs of Childhood and Youth: "So many people gave me something or were something to me without even knowing it. . . . I always think that we all live spiritually, by what others have given us in the significant hours of our life. These significant hours do not announce themselves as coming but arrive unexpectedly."