If you want answers like who/what or even why or how... do yourself a favor - don't watch it. Even if you didn't like the movie Blindness (2008) don't go for it. If you are OK with all that, than maybe you'd like it.

In my case I felt entertained despite some disturbing elements: 1. The blind car driving scene that is almost ridiculous 2. "Slight" similarity with Dawn of the Dead (1978) 3. Really bad performance by Danielle Macdonald. 4. All the women actresses had a perfect make-up. Come on... the world is at end and they have enough time for their mascara...