Every great artist has themes and obsessions he returns to throughout his work. You won’t find many themes as unsettling as the one the great English novelist Ian McEwan has made a specialty: children in distress. In THE CEMENT GARDEN, the father and then mother of four young siblings die, and the children encase their mother in cement so that the authorities won’t put them in an orphanage. THE CHILD IN TIME begins with the supermarket abduction of a three-year-old girl. Now, in THE CHILDREN ACT, his best work since 2007’s ON CHESIL BEACH, McEwan gives us a 17-year-old boy who will die from leukemia unless he receives an emergency blood transfusion.

But while the child in distress is the pivotal point of the action, the novel is about something more profound. THE CHILDREN ACT is also a portrait of an accomplished woman at a moment of crisis. Fiona Maye is a High Court judge who works in London’s Family Division. She and her husband, Jack, a professor of ancient history, have been married for more than 30 years. Fiona’s career never gave her time to have children, and she now regrets this decision. She feels her childlessness most keenly when she presides over cases involving children, including a recent case in which a divorcing Hamedi husband and wife disagree over their two daughters’ education, and a case in which she decides to order the separation of Siamese twins, knowing that the surgery will kill one infant brother to save the other.

"...[McEwan's] best work since 2007’s ON CHESIL BEACH... Few authors have McEwan’s gift for unnerving readers with provocative plots.... In Fiona, McEwan has created a powerful portrait of a woman in turmoil, over her legal decisions as much as her marriage."

At the start of the novel, Jack announces that he wants to have an affair with a 28-year-old statistician. He is dissatisfied with the infrequency of his and Fiona’s sexual relations. “I’ve become your brother,” he says. “It’s cozy and sweet and I love you, but before I drop dead, I want one big passionate affair.” He’s right about Fiona’s diminished interest in sex; stress over her cases occupies her thoughts to the exclusion of all else. But Fiona is devastated by Jack’s news and warns that the affair will be the end of their marriage.

Later that evening, Fiona receives a call from her clerk. Counsel representing the Edith Cavell hospital has requested that Fiona grant an order to allow them to give a blood transfusion to 17-year-old Adam Henry. Adam and his parents are Jehovah’s Witnesses and have refused to consent to the transfusion on religious grounds. Fiona orders a hearing for 2pm Tuesday, the day before Adam’s condition will have deteriorated to the point where a transfusion would do no good.

As nurses, the social worker and Fiona admit, Adam Henry is an extraordinary child. All of them predict that, if he lives, he will have a great future. Adam writes poetry and can play Britten pieces on the violin after only four weeks of practice. My only complaint about the book is that the moral quandary driving the plot wouldn’t have been as stark if McEwan had put a less exceptional teenager at its center. The question “Is a person’s life worth saving despite the person’s wishes?” would have been more complicated for some readers if Adam hadn’t been so gifted.

The remainder of this short novel chronicles the hearing and the events that occur after Fiona renders her judgment. It doesn’t give the story away to say that the important point of THE CHILDREN ACT is not Fiona’s decision in the Adam Henry case but the repercussions of that decision. “Repercussions” would have been an appropriate, if less catchy, alternative title for the book, as most of the characters make decisions that alter lives other than their own.

Few authors have McEwan’s gift for unnerving readers with provocative plots. Abducted toddlers, mothers in cement, cancer-plagued teens --- he knows how to strike a nerve. In Fiona, McEwan has created a powerful portrait of a woman in turmoil, over her legal decisions as much as her marriage. And the cool precision of his writing adds to the effect. Early in the novel, we learn that Fiona is known for her “crisp prose, almost ironic, almost warm, and for the compact terms in which she laid out a dispute.” The same can be said of Ian McEwan.