Star Trek The Next Generation, book 41 : Invasion #2: The Soldier of Fear
Dean Wesley Smith et Kristine Kathryn Rusch1996

Long ago, before the dawn of civilization, they were banished to the realm of nightmares. Now the terrors are real...

A generation ago, another Starship Enterprise fought off a ship of exiled aliens intent on conquering all of the Alpha Quadrant. Starfleet thought the foe had been repelled forever -- until now. The Furies have returned in mighty warships even more powerful than before. But their weapons are more than merely physical, for these aliens are the origins of all the demons and monsters of ancient myth, and they have found a way to project fear directly into the minds of their enemies. To defeat the Furies, and save the Federation, Picard and the crew of the USS Enterprise must first conquer the darkest terrors of their unconscious minds.

Book Two of the most exciting crossover epic of all time!