Provenance of Shadows — David R. George III

IN A SINGLE MOMENT
. . . the lives of three men will be forever changed. In that split second, defined paradoxically by both salvation and loss, they will destroy the world and then restore it. Much had come before, and much would come after, but nothing would color their lives more than that one, isolated instant on the edge of forever.

IN A SINGLE MOMENT
. . . Leonard McCoy, displaced in time, saves a woman from dying in a traffic accident, and in so doing alters Earth's history. Stranded in the past, he struggles to find a way back to his own century. But living an existence he was not meant to, he will eventually have to move on, and ultimately face the shadows born of his lost life.

IN A SINGLE MOMENT
. . . Leonard McCoy, displaced in time, is prevented from saving a woman from dying in a traffic accident, allowing Earth's history to remain unchanged. Returning to the present, he encounters a medical mystery he is committed to solving. But the echoes of an existence he never lived haunt him, and the specter of a premature death will bring him full circle to the shadows he has never faced.