Shadows on the Sun

Summary
From the back cover: As a young doctor with a beautiful family and a promising medical career, Dr. McCoy thought he had it all. But when the woman he loved betrayed him, McCoy fled to Starfleet hoping to lose his pain in the depths of space. Now, more than forty years later, the USS Enterprise and her crew are ordered to transport a group of mediators to the planet Ssan, a world where assassination is a long and time honored tradition.

Dr. McCoy is surprised to learn that his ex-wife, now remarried, is one of the mediators. But before McCoy can begin to face his feelings for his former love, she and Captain Kirk are trapped by a band of deadly assassins. Suddenly, McCoy is in the center of an explosive civil war, where he is the only one with the power to save the woman who once nearly destroyed him. McCoy must now overcome a centuries long tradition of death, and his own past with the woman he still loves, or else lose her for the second time...