Frank, played by Lou Diamond Phillips, awakens in the woods, dangling from a rope by one leg. He also has some sort of bleeding head injury. Alone in the woods, he manages to sever the fraying rope that is holding him captive, but he was hanging in the air from a tree limb about 15 feet up. Thankfully, it is fall so there is a mattress of dried leaves to keep him from breaking his neck. He starts yelling to see if anyone is around.
Eventually, his wife Natasha's coworker Andy comes along in his office attire. Frank doesn't remember who he is and he needs help. Andy isn't there to help; Andy is angry and Andy has a gun. He starts yelling, "Where is she?" and pushing Frank.
All Frank has been able to discover is that he's holding a bloody knife with the name Tom Martin on it; he found his driver's license in his wallet and knows his name is Frank Hill. He's having flashbacks of shooting and blood back at a cabin. Andy keeps yelling at Frank that he murdered people and that he has done something with Andy's wife Natasha.
Frank and Andy stumble around the woods for hours. Frank's hurt leg is slowing him down. Andy's dress clothing is slowing him down. They finally find a half-dead park ranger. The name plate on his jacket matches the name on the knife Frank is carrying. The man's throat is slit and he is spurting blood. Andy keeps telling Frank, "You did this."
Since no medical help is available, Frank begs Andy to shoot the ranger to help him die. Andy starts looking really uncomfortable. We learn there are no bullets in the gun. Having been terrorized with that gun for hours, Frank snaps and kills Andy. He backs him against a weathered barn and slits his throat. An arterial spatter extravaganza follows and then Frank walks away from the scene. The viewer is left wondering whether Frank or Andy did the killings at the cabin and stabbed the ranger.
Andy wasn't dressed for a vacation in the woods and had a car one would not take camping. Andy had no wedding ring and couldn't find his way through the woods, though he claimed to have been there before; he also had the gun. Andy kept telling Frank, "You did this" when referring to the murders at the cabin and the death of the park ranger.
Frank had a wedding ring and pictures of his wife Natasha in his wallet. His leg was injured. The only weapon he had was Tom Martin's knife, which was probably planted on him. Frank, even with his amnesia, had an easier time finding his way through the woods. He later remembered that Andy had been stalking Natasha at work.
In the end, Andy is a much more likely suspect. He eventually drove Frank to murder him. I think Andy did all the killings at the cabin because he couldn't have Natasha for himself and was jealous because Frank did. He wanted to ruin Frank's life and possibly send him to prison by manipulating Frank's fragile memory until Frank thought he was responsible for the string of murders.