Stickyandhotfromthelongdrivetovisitarelativeattheirnewlyacquired,remote,ruralfarmhouse,SamandJason,ayoungcoupleonvacation,decidetoswiminapondtheyfindattheendofafreshlycutpath.Whileswimming,Jasonisbittenbyastrangeleech-likeorganism.Whenheattemptstoremovethecreature,partofitripsoffandcrawlsinsidehisleg.Backatthehouse,Sam’ssisterandherfamilyhaveyettoreturn.Astimeprogresses,theinjuryonJason’slegworsensintoarapidlyspreadinginfection,andstrangecluesbegintorevealthattheremaybemoretotheirhost’sabsencethanitpreviouslyappeared.ItsoonbecomesaraceagainsttimetodiscoverwhathappenedtoSam’ssisterandherfamilyandwhatliesinstoreforJason,facedwithhisphysicalandemotionaldisintegration.