Shadows of Angels — Matt Larkin

Rachel has found the Angel's Ark, the greatest repository of knowledge and power in the known universe. Now her enemies multiply as countless factions struggle to take it from her. She dares not let anyone possess such a weapon, but her opponents won't hesitate to use those closest to her. She has only one person left to rely on: the Gehennan mercenary, Knight, a former assassin of terrifying brutality. But before he can save Rachel, Knight must overcome the shadows of his own past.