Claire is only seven years old when her college-age sister Alison vanishes from the luxury resort on the Caribbean island of Saint X on the last night of her familys vacation. Several days later Alisons body is found in a remote spot on a nearby cay, and two local men, employees at the resort, are arrested.

But the evidence is slim, the timeline against it, and the men are soon released. Its national tabloid news, a lurid mystery that will go unsolved, but for Claires family there is only the sad return home to broken lives.

Years later, riding in a New York City taxicab, Claire recognizes the name on the cabbies licence, Clive Richardson her driver is one of the men originally suspected of murdering her sister. The fateful encounter sets her on an obsessive pursuit of the truth, not only what happened on the night of Alisons death, but the no less elusive question of exactly who was this sister she was barely old enough to know: a beautiful, changeable, provocative girl of eighteen at a turbulent moment of identity formation.

As Claire doggedly shadows Clive, hoping to gain his trust, waiting for the slip that will uncover the truth, an unlikely intimacy develops between them, two people whose lives were forever marked by a tragedy.