In 2006, John Boyne's novel "The Boy in the Striped Pajamas" broadened the minds and broke the hearts of thousands of young readers — and more than a few old ones, as well. The Irish writer's bestseller told of the friendship between Shmuel, a Jewish boy in Auschwitz, and Bruno, the young son of the concentration camp commandant. Boyne's take on the Final Solution consisted of flashes of light in engulfing darkness — humanity amid barbarity — which made for an unsettling yet riveting read.

Boyne's latest novel, "All the Broken Places," is not so much a follow-up as a spinoff, and one that is aimed squarely at adults. Its narrator is 91-year-old widow Gretel Fernsby. "You're a dark horse," someone tells her. "Darker than most," is her reply. For Gretel is Bruno's sister. Haunted by his death and scarred by her father's war crimes, she has lived a life of grief and guilt, spending large parts of it on the move and under assumed names.

For decades, though, she has been comfortably settled in London's affluent Mayfair. Her equilibrium is disrupted when she gets to know her new neighbors in the flat downstairs. After taking stock of a catalog of bruises, black eyes and distressing behavior she realizes that the man of the house, film producer Alex Darcy-Witt, is abusing his wife, Madelyn, and his 9-year-old son, Henry.

Further worries manifest themselves: Gretel's other neighbor, Heidi, is becoming increasingly forgetful; and Gretel's cash-strapped, much-married son, Caden, is determined to sell her luxury flat.

Boyne's narrative alternates between Gretel's present and key events in her troubled past. At the end of the war, when she is 15, she and her mother flee Germany for Paris. Both soon learn to their cost that some residents are actively hunting Nazis and their collaborators, and are prepared to take the law into their own hands in their quest for justice.

Later, at age 21, Gretel leaves Europe to make a fresh start in Australia. However, a chance encounter with her father's former personal aide — "the monster's apprentice" — leads her to commit a drastic act and seek new sanctuary. Then in London in 1953, she finds love with a Jewish man called David — until she comes clean to him about her true origins.

At various stages in Gretel's life, Boyne explores his main themes: parent-child relationships; complicity and culpability — to what extent the sins of the father are to be laid upon the children; and the equally thorny matter of atonement. Boyne intensifies the drama by throwing in some deft twists (a nasty shock in the Paris back story, a happy family revelation in the present-day strand) and ramping up the tension in a climactic showdown which sees Alex threatening to expose Gretel.

This is a powerful page-turner, a novel that tackles complex issues while keeping its reader utterly gripped. Gretel's "final story" is an essential one.

Malcolm Forbes has written for the Times Literary Supplement, the Economist and the Wall Street Journal. He lives in Edinburgh, Scotland.

All the Broken Places

By: John Boyne.

Publisher: Pamela Dorman/Viking, 387 pages, $28.