Star Trek: The Lost Era (2298): The Sundered

Five years after the presumed death of Captain James T. Kirk, the U.S.S. Excelsior, commanded by Captain Hikaru Sulu, is at the forefront of exploration, diplomacy, and the defense of the Federation.
Unprecedented peace talks with the violently xenophobic Tholian Assembly trigger a deadly confrontation aboard the Excelsior. Now Sulu and his crew -- including Chekov, Rand, Chapel, Tuvok, and Akaar -- are thrust into an unexpected conflict between the Tholians and a mysterious new enemy, the Neyel...whose origins, if revealed, could lead to war with Earth itself.

As the Tholians weave a web of vengeance, the Excelsior is flung beyond the galaxy to discover the hidden truth about the alien Neyel, forcing Sulu to question where his responsibilities lie -- with the fragile peace he must preserve, or with the victims of his own world's tragic past.