Cowl is a time travel novel, more or less. In the future there ar two factions at war, the Heliothane Dominion wins although a number of the enemy manage to slip into the distant past in order to snatch victory from the jaws of time, as it were. The leader of this enemy faction is Cowl, who has seeded the timelines with Tors, which are organic time machines that attach themselves to whomever finds them and then begin shifting those individuals back through time to Cowl and his beast, who feeds on these individuals to grow strong enough to disrupt the future victory, perhaps destroying Earth in the process.

(Source: Tor Books)