All the Flowers Are Dying — Lawrence Block

Scudder, a complex character who has grown and aged in real time, confronts the implacable challenge of mortality. But he must also tackle a determined, relentless, and icily inhuman adversary, perhaps the most unforgettable villain Block has ever created.

A man in a Virginia prison awaits execution for three hideous murders he swears, in the face of irrefutable evidence, he did not commit. A psychologist who claims to believe the convict spends hours with the man in his death row cell, and ultimately watches in the gallery as the lethal injection is administered. His work completed, the psychologist heads back to New York City to attend to unfinished business.

Meanwhile, Scudder has just agreed to investigate the ostensibly suspicious online lover of an acquaintance. It seems simple enough. At first. But when people start dying and the victims are increasingly closer to home, it becomes clear that a vicious killer is at work. And the final targets may be Matt and Elaine Scudder.