Exodus - Josepha Sherman

Ambassador Spock has married his fellow Vulcan Starfleet officer, Captain Saavik, but he and his wife have little time to enjoy their newlywed status before both of them are plunged into the heart of a clandestine war. Pursuing his hope of uniting Vulcan and Romulus after centuries of hostility between them, Spock finds himself inadvertently drawn into conflict with a long-lost race -- also of Vulcan descent -- who are set on the destruction of the weakened Romulan Empire.
Together with the surviving members of Captain James T. Kirk's old crew, Spock and Saavik are forced to abandon the aegis of the Federation and wage their own secret war behind the scenes. And even as their relationship deepens, their future is threatened as Spock's dream of peace leads him into deadly danger