Amazon.com Product Description (ISBN 0743491696, Mass Market Paperback)

...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.

...Spock, displaced in time, watches his closest friend heed his advice by allowing the love of his life to die in a traffic accident, thereby preserving Earth's history. Returning to the present, however, Spock confronts other such crises, and chooses instead to willfully alter the past. Challenged by the thorny demands of his logic, he will have to find a way to face his conflicting decisions.

...that stays with Spock, he preserved the timeline at the cost of Jim Kirk's happiness. Now, the death of that friend will cause Spock to reexamine the fundamental choices he has made for his own life. Unwilling to accept his feelings of loss and regret, he will seek that which has previously eluded him: complete mastery of his emotions. But while his quest for the perfect geometry of total logic will move him beyond his remorse, another loss will bring him full circle to once more face the fire he has never embraced.