Eight teenagers, including Brady Turner [Mark McLachlan], Claire Martin [Caitlin Martin], Duncan McKay [Chris Solari], Kit [D.W. Reiser], Annabelle [Julie Mintz], Sunny [Sommer Knight], Foster [Rhett Wilkins], and Hubs [Greg Wayne], head to a remote lake in Southern California for spring break. As they prepare to depart, Sheriff Bowman [Harrison Young] warns them to be sensible and stay out of danger.
During a day of partying, they gather around a bonfire while Kit recounts a local legend from the early 20th century about Harlan, a hotel owner who kept a 40-foot crocodile named Flat Dog at his hotel. Harlan builds a shrine to Flat Dog, treating her as an avatar of Sobek, the ancient crocodile god, and this devotion spawns a small cult. The townspeople eventually drive him away and torch his hotel, while nearby two fishermen destroy a crocodile nest only to be attacked and eaten by Flat Dog.
The next day, the group resumes their festivities. Annabelle's dog Princess runs off, leading the friends to the crocodile’s nest where Duncan breaks an egg and Hubs hides the last one in Claire's bag. That night, Sunny becomes extremely drunk and reveals Brady cheated on Claire with her, causing Claire to break up with Brady. Hubs, also intoxicated, falls asleep by the bonfire, and the others return to the boat. Later, Hubs attempts to reunite with the group but is eaten by Flat Dog, while the boat becomes untied and starts to drift on the lake.
In the morning, the boat is stuck, stranding the friends. While some try to fix it, Brady and Sunny go to search for Hubs. Sunny tries to coax Brady into swimming, but they narrowly escape an attack by Flat Dog. They rush back to warn the others, but Flat Dog arrives and sinks the boat, killing Foster.
Sheriff Bowman finds the fishermen’s remains and Hubs, then visits Shurkin [Terrence Evans] and Lester [Adam Gierasch], two locals who handle alligators. Shurkin sets out with the Sheriff to find Flat Dog and kill her to avenge his grandfather’s and father’s deaths, while Lester is seen feeding her but is eventually devoured himself. As night falls, the teenagers remain stranded in the woods. Flat Dog returns, and Sunny is eaten. The survivors reach a small shop, where Brady tries to phone the Sheriff, but Flat Dog breaks through a wall and devours Annabelle. Kit escapes to start the truck outside, while Brady, Claire, and Duncan fight the crocodile. A fire breaks out, causing the truck to explode and killing Kit, while scaring Flat Dog away.
The next day, the Sheriff and Shurkin find Brady, Claire, and Duncan and pick them up on their boat. Soon after, Flat Dog locates them again. Shurkin is knocked into the water and eaten, followed by the Sheriff, who is killed as well. With the boat’s engine broken, the survivors swim to land. Claire discovers Flat Dog’s last egg in her bag, and they use it as bait to lure the crocodile to them so they can kill it. When Flat Dog arrives, Duncan attempts to strike but is swallowed whole, only to be regurgitated moments later after being covered in bug spray. Claire hands Flat Dog the egg, which hatches into a baby crocodile, then she returns to her nest, leaving Claire, Princess, Brady, and Duncan free to escape.
