This is book number 47 in the In Death series.
Two young children disappear from their East Side home in New York City, their nanny killed in cold blood. As Lieutenant Eve Dallas begins to unravel the crime scene and search for Henry and Gala MacDermit, she's drawn into the twisted mind of a kidnapper who will stop at nothing to take revenge. Horrific threats concerning the brother and sister hit far too close to home for Eve, drawing her back into memories of her own tortured childhood.
But Eve knows that there's no time to waste on the past, and with every passing hour her determination to bring the children safely home strengthens. Eve and her team find themselves following an electronic breadcrumb trail left by a boy desperate to escape the evil witch. Their investigation into the kidnapper's sordid past reveals violent coercion, ritualistic killings, and chilling bloodlust--making her terrifying plans for the children abundantly clear.