This is a very interesting film which holds you tightly from its beginning by confusing you and teasing you with flashbacks of minor hints.
Essentially a man wakes up in a mass grave and manages to climb out of it with some assistance from a stranger who then promptly runs away. He makes it to a house and comes upon a group of other people. The main problem for them all is that none of them can remember who they are or why they are there. They do not understand why the area is littered with corpses or generally why no one else is about..
To explain much more of the plot would ruin it for you! All I can say is that what looks considerably B-grade as it starts (and pretty much reads as such) is a very interesting film well worth watching.