Humans call the crystalline creatures Sirens. They can kill with a scream. Decapitate with a single slash of their cutting fins. The aliens are the most vicious life form Earth has ever encountered, and Scott has one trapped in his mind. Her name is Water, and her hatred for Scott's species is only matched by her desire to be free of him.

Scott couldn't agree more, but neither of them understand the cost of letting her out.

In order to save their sanity, Scott and Water have to save her people.