Jewels Of Atlantis by Gena Showalter

All Atlantis seeks the Jewel of Dunamis, which legend claims can overcome any enemy. Grayson James, human agent of the ultra-secret Otherworld Bureau of Investigation has orders to keep it from the wrong hands -- or destroy it. What he doesn't know is that Jewel is a woman, not a stone! But once he meets this precious gem, destroying her is the last thing on his mind....

Jewel, part goddess, part prophet, is a pawn in Atlantis's constant power struggles. She needs Gray's help to win freedom and uncover the secrets of her mysterious origins. Gray needs her wisdom to navigate monster-ridden Atlantis. But need blossoms into passionate love as they fight demons, dragons, vampires -- and a prophecy that says the bond between them could destroy them both.

If you haven't ordered this yet, all I can say is...why not?