Forget anything you ever heard about possession, exorcisms, salt circles and pentagrams. The modern demon is far more difficult to catch - and even harder to destroy. After the savage, tragic deaths of their parents, Grace and Joe Callahan learn that they are descendants of the sarsareh - an ancient order of mercenaries who hunt very special prey. Grace and Joe take their place in the Order, but are treated with hostility and fear by other recruits. For the Callahan siblings have powers that fascinate and terrify. Joe is a Ferryman, capable of opening dimensional rifts, while Grace's telepathic abilities surpass anything the Order has ever seen. To complicate matters, Grace falls for her older, more experienced squad leader, Ivan. Meanwhile, the sarsareh elders have their own plans for Joe. But none of that will matter if the powerful demon Mammon manages to convince Joe to open a gateway to his demon world and overrun Earth with his armies. If he succeeds: game over.