The Imaginary Five — D.J. Goodman

A mysterious woman wanders in the wasteland of a future world, until a man from her past finds her. They are both legends from another time, and he needs her help to stop the darkness that is growing in the world. The two of them, along with a man who prefers the cold, a creature from the shadows, and a woman obsessed with teeth must find the thing trying to destroy what's left of the world...a thing known only as Cthulhu.