Dark Infinite — Ann Martin

Christopher Bartholomew has visions so painful, they nearly drive him to madness. When he sees that Ashka, ruler of the Nexum underworld and keeper of the Stone, has been murdered, he knows something far worse is coming, for the Stone allows travel between underworlds and Earth. Someone or something will come looking for it. Now the Stone is in his hands and he must keep it safe, no matter the cost. Yet the visions continue, and it takes everything he has to keep it together. How much more can he endure before the beast within him claws its way out?

After a vicious attack by something she doesn't understand, Mackenzie Wallace lays at Death's door. When Christopher find her, he takes her blood, her body, and gives her something unexpected--a second chance at life. She discovers his world, where every battle is to the death, and it terrifies her. Yet, she's determined to carve a place for herself in this new world, to become more than she ever could've thought possible. As she hones her new skills with swords and knives, she realizes all too quickly that immortality doesn't mean invincibility.

Christopher discovers a coven of ancient sorcerers has risen from Toth, the underworld reserved for the darkest of sorcerers. Now freed from the confines of the underworld, they will bind their minds and lives to the demon of Dark Infinite to, once again, become Circle of the Twelve. Feared for their power in ancient times, they will unleash Dark magick upon the Earth to forge a new world order.