Dreams of the Raven

Summary
From the back cover: A merchant ship's frantic S.O.S. sends the Enterprise speeding to the rescue! But the starship's mission of mercy soon becomes a desperate struggle of survival against a nightmarish enemy Captain Kirk can neither identify nor understand, an enemy he must defeat without the aid of one of his most trusted officers.

For the Leonard McCoy Kirk knew is gone. In his place stands a stranger - a man with no memory of his Starfleet career, his family, his friends or the one thing James T. Kirk needs most of all...

His dreams.