Livewire by Harlan Coben

In Livewire Harlan Coben returns to his sports agent and former professional basketball player Myron Bolitar.  Myron agrees to help his pregnant tennis star client Suzze T find her rock-star husband Lex who disappeared after a facebook post declared that he was not the father of the baby.  Myron finds Lex in a nightclub with Kitty Bolitar, Myron’s sister-in-law who disappeared with his brother years ago.  Kitty is high on heroin, but she manages to run away from Myron.  Desperate to find his brother, Myron plunges into a world dominated by drug dealers and mafia with his vigilante friend Win watching his back.