Sword of Damocles (Star Trek: Titan, Book 4)

Captain Riker and his crew have discovered a mysterious planet populated by a civilization where science and faith are struggling for supremacy, due in large part to a strange, unexplained phenomenon known as the Watchful Eye, visible in the sky above the planet. Two teams from the Titan have been sent to investigate. One must covertly observe the people and culture of the planet while the other team takes a shuttle to study the strange Watchful Eye. But when the team on the planet is discovered, a dramatic chain of events is set in motion and cause and effect collide, creating a temporal paradox which threatens both the past and Titan's future.