Darkest Fear - Harlan Coben

Myron Bolitar's father's recent heart attack brings Myron smack into a midlife encounter with issues of adulthood and mortality. And if that's not enough to turn his life upside down, the reappearance of his first serious girlfriend is. The basketball star turned sports agent, who does a little detecting when business is slow, is saddened by the news that Emily Downing's 13-year-old son is dying and desperately needs a bone marrow transplant; even if she did leave him for the man who destroyed his basketball career, he wouldn't wish tsuris like that on anyone.