Sam and Jason, a young couple on vacation, decide to swim in a pond they find at the end of a freshly cut path. While swimming, Jason is bitten by a gruesome leech-like organism. When he attempts to remove the creature, part of it rips off and crawls inside his leg. Back at the house, Sam's sister and her family have yet to return. As time moves on and the injury on Jason's leg worsens into a rapidly spreading infection he starts to hallucinate. Strange clues begin to reveal that there may be more to their host's absence than previously appeared. It soon becomes a race against time to discover what happened to Sam's sister and her family and what lies in store for Jason.