Reaper - The Gatekeepers, #1

Aaron and Kyle have just learned two things: the world is full of unseen magical creatures, and some of them are rather angry. As the newest members of the Gatekeepers, they must race around the world, and against the clock, to stop the Lord of the Damned before he enslaves every living being to his wicked will. Their fight will take them to Hell and back, but regardless of whether they win or lose, their world will never be the same again.