?Demons by J. M. Dillard
A research expedition unearths a mysterious artifact on a distant planet, and soon thereafter members of the team meet with suspicious deaths, one after another. Those deaths continue after some of the survivors return to Vulcan, and it soon becomes clear that an alien force has possessed others, including Spock’s own father, Sarek. (Ultram) Spock and the other crew of the Enterprise must defeat the demons to save Vulcan, and to prevent them from using the ship to spread their invasion throughout the galaxy.
