Darkest Fear - Coben Harlan

Life isn't going well for Myron Bolitar. His business is struggling, and his father, recently recovered from a heart attack, is facing his own mortality - and forcing Myron to face it too. Then Emily Downing, Myron's college sweetheart, reappears in his life with devastating news: her thirteen-year-old son Jeremy is gravely ill and can be saved only by a bone-marrow transplant - from a donor who has vanished without trace. Before Myron can absorb this revelation, Emily hits him with an even bigger shocker: Jeremy is Myron's son, conceived the night before Emily's wedding to another man. Staggered by the news, Myron plunges into a search for the missing donor. But for Myron, finding the only person who can save the boy's life means cracking open a mystery that involves a broken family, a brutal kidnapping spree, and a cat-and-mouse game between an ambitious reporter and the FBI.