Star Trek: The Next Generation (Book 40): Possession

Plot

Eighty years ago, bodiless entities brought a plague of violence and bloodshed to the planet Vulcan. The nightmare ended only when the entities were trapped inside special containers. Now, on the eve of a galaxy-scale scientific exposition, the containers have been opened, freeing the malevolent entities to possess the minds and bodies of all they encounter, including the crew of the "Starship Enterprise"(TM) . Friends turn into foes, and no one can be trusted as Captain Picard faces a deadly and insidious threat. Unless the entities can be stopped once more, they will spread their madness throughout the entire federation.