Time's Enemy

Buried in five-thousand-year-old debris, the Defiant crew finds the wreck of their own ship, destroyed, apparently, in a battle fought at the dawn of the Alpha Quadrant's history. Sisko has to work out when and how the Defiant is fated to be thrown back in time to that ancient war, and whether the side that won it has already come back to finish what it started. Part of the four-book Invasion! crossover event.