East of Vienna, a canoe trip down the length of the Danube River turns strange and horrifying. The two men traveling find it bad enough when they are forced to camp on an isolated island in the middle of nowhere while gale-force winds howl and waters rise. But soon, the threats take on a supernatural tinge. Wild sounds and visions in the night convince the men that they're being hunted by beings from another dimension, who are not so much malicious as vastly, cosmically indifferent to their welfare-and hungry.