The film start with a boy run to a small town to find a doctor to help his village deep in the forest. A man (or group) go with him, and when he come he discover something more sinister. The village seem primitive, as when the boy come back he then change back to his normal loincloth as everyone else (before he dress in short and shirt when he go find the doctor). Something try to kill them one by one. It turn out that some kind of humanoid monster can turn invisible are responsibility for this. They fought, and in the end able to kill it near a lake (or river) by bait it go to there to reveal it from it’s invisible ability. (if i recall correctly they kill it with a rocket launcher)