Within the course of a week spanning March and April 2007, a serious, untoward event in the health of three strangers, two of whom lost their lives, was destined to impact the lives of hundreds, even thousands of people in a complicated web of causality. The victims had no premonition of their individual tragedies. Though they were all generally healthy married men of similar ages, they were engaged in totally different occupations, and each had absolutely no knowledge of the others, either socially or through business. One was a Caucasian physician who experienced a painful and debilitating athletic injury; the second an African-American computer programmer who contracted a fulminant, and rapidly fatal, nosocomial postoperative infection; and the third was an Asian-American accountant who suffered a ruthless, execution-style death.

LIKE MOST PEOPLE, Dr. Jack Stapleton never truly appreciated the anatomical and physiological marvel of his knees until they gave out, on the evening of March 26, 2007. He'd been at work as a forensic pathologist at the Office of the Chief Medical Examiner, or OCME, since early that morning. He'd commuted to and from the OCME on his beloved Cannondale mountain bike without once acknowledging the contributions of his knees. During the rest of the morning, he'd done three autopsies, one of which was a complicated affair involving painstaking dissection of the tracks of multiple gunshot wounds. In total, he'd been on his feet in the autopsy room, colloquially referred to as "the pit," more than four hours, moving by reflex to aid him in his work. Never once did he think about his knees and the effort expended by their various ligaments, which faithfully maintained the integrity of the joints despite the considerable stresses placed on them, and by the menisci, which cushioned the substantial pressure exerted by the distal ends of the femurs, or thighbones, on the tops of the tibias, or shinbones.