Darkest fear. Harlan Coben. 2002.

Life isn’t going well for Myron Bolitar. His business is struggling, and his father recently suffered a heart attack when, out of the blue, Myron’s college sweetheart, Emily, appears. Her thirteen-year-old son Jeremy is gravely I’ll and can be saved only by a bone-marrow transplant from a donor who has vanished without trace. Then Emily reveals even more shocking news: Jeremy is Myron’s son, conceived the night before Emily’s wedding to another man.

Staggered by the revelation, Myron plunges into a search for the missing donor - and gets caught up in a brutal kidnapping and a cat-and-mouse game between an ambitious reporter and the FBI.