Demons
Jeanne Kalogridis
 A strange device found by a scientific expedition is taken to the planet Vulcan. It begins taking people over one by one, replacing them with malevolent power-hungry entities. The crew of the Enterprise, those not yet replaced, must contain this threat to Vulcan and defeat it. This story is continued in the Star Trek: The Next Generation novel Possession, also by J.M. Dillard, where it is revealed the device is one of many.