After actually surviving the events of LP3, Reba (Yancy Butler) is now the game warden of the now sealed off Lake Placid, trying to figure out the mutation in order to eradicate the monster size crocodile problem once and for all. Nevertheless, a series of events causes a group of high school students to accidentally enter the preserve.
In the end, a lot of people get killed before it is revealed that Jim Bickerman (Robert Englund) has apparently been helping the crocodiles continue to thrive. Bickerman gets away with a bag of croc eggs but they crack and he is eaten by a large crocodile.
In the end, Theresa Clove (Elisabeth Röhm), her daughter Chloe (Poppy Lee Friar), Max Loflin (Benedict Smith), Ryan Loflin (Paul Nocholls), and Reba are the only survivors.
The lake is later declared Croc free by the government but we see jogger get attacked and killed by one, signifying that the problem will probably never be solved.