From the liner notes

1917. The Western Front. A handful of survivors from Y-Company are utterly lost in enemy territory. They find shelter in an abandoned enemy trench - a claustrophobic maze of blind corners and underground tunnels, overflowing with war dead and infested with rats. It is here the survivors of Y-Company wait to be rescued. But as night draws nobody comes. They begin to think there is someone ...or something in the trench with them. One by one the young men of Y-Company die as the unseen stalker terrorizes and preys upon their fear.