Black Fire (novel)

Summary
From the back cover: There is sabotage aboard the Enterprise, and Spock's investigation leads him into defiance of the Federation and a bizarre alliance with the Romulan and Klingon Empires against the bloodthirsty Tomarii - a savage race for whom war and battle are life itself.

Now Spock has been declared a traitor and condemned to the shame of the Federation's highest security prison. And now Captain James Kirk must face the toughest decision of his command, while a lifelong friendship and the destiny of the free universe hang in the balance!