Good read, book 2 in The Horde Wars series. The heroine stumbles into one of the battles between the Shikar and Daemons and is sent to the Shikar fortress for protection. The hero is part of the team of Cady and Obsidian [book 1, Ravenous] and as an Incinerator he wields the power of fire. She does not wish to give up her life in the world above and insists on returning, even though she is told that the Daemons will probably come hunting her. Cinder refuses to let her go unprotected and moves in with her. Sex between these two sometimes literally 'burns up the sheets'.
More intriguing hints are dropped about the Shikar and the world they inhabit...
There is an ongoing story arc; read them in order.
Sacred Eden in the Manaconda anthology
Lord of the Deep
Shikar stories, taking place in the world of the Horde Wars
Caress of Flame
Ride the Lightning