Researchers Frank Mills and Tillman drift across the lake on a rubber tube raft, but a sudden tug yanks [Tillman] into the water and leaves behind a hand and a foot, signaling that something fierce lurks below. In Aroostook County, Maine, James Riley, the local sheriff, is shown the grisly evidence as Frank reports the grisly findings. James, Frank, and wildlife officer Emma Warner venture out onto the lake and soon uncover more of Tillman’s remains, escalating the mystery and danger.
Meanwhile, three friends Mike, Edie, and Sharon are depicted hiking through the forest, disappearing into the lake after stopping to swim. James, Emma, and Frank eventually stop at the house of Sadie Bickerman, an elderly hermit rumored to feed crocodiles, but she refuses to answer their questions or let them in. It doesn’t take long for the investigators to realize that a giant crocodile is behind the escalating terror, especially after its attack destroys their boat and leaves them scrambling to safety. A poacher named Struthers and his assistant Ahmad arrive by plane, hoping to hunt the crocodiles after receiving a tip from a local.
The sheriff’s son, Scott Riley, wanders into the woods and seems to be stalked by the approaching creature. He soon meets Kerri and her boyfriend, Thad, while Daisy, the dog belonging to Kerri, barks at something moving in the lake—though Kerri herself sees nothing definitive. Sadie converses with a photographer at a boat dock before retreating to her cabin; the photographer is killed by a crocodile while taking pictures, underscoring the peril that surrounds them all.
During a boat ride, James slows the vessel, hurling [Frank] into the water, but the pair manage to haul him back aboard. When a crocodile surfaces, James raises his gun, only for the beast to dive beneath and topple the trio into the water again. They reach land unharmed, and soon cross paths with Struthers and [Ahmad], who had flown in to distract the giant predator with their aircraft.
A new scene introduces Rachel and Larry alongside Scott, Kerri, and Thad as they explore another corner of the lake. With them are the sheriff’s team and Deputy Dale Davis, who helps unload the boat and set up camp for the night. A wild boar becomes an unwitting meal for the crocodile, and the group’s gunfire only momentarily slows the creature as Deputy Davis struggles with the rope securing its jaws before the beast tears loose and devours him. [Frank] dies from a fall, adding a new layer of grief to the already perilous situation.
Rachel and Larry are killed in a brutal strike, while the younger trio—Scott, Kerri, and Thad—discover eggs in the woods. Thad breaks some of the eggs, and is swiftly killed by a crocodile. The group tries to bait the crocodile with a boar carcass, but a harpoon arrow damages [Struthers]’ plane, sending him into a precarious fate. James and Ahmad abandon the plane, and Struthers is tossed from it, though Ahmad eventually neutralizes the crocodile. Thunderstorms rage through the night, forcing everyone into tents for protection, and Scott and Kerri are left stranded with Larry, who is horrified by the events.
By morning, Scott, Kerri, and Larry climb a tree to escape a third crocodile, but tragedy strikes when Larry falls and is killed. James locates the two surviving teenagers and defeats the crocodile using a grenade launcher. Sadie, who has revealed that there are actually four crocodiles, lures the remaining predators toward the lake and is herself devoured by one. The police engage another crocodile, and Emma punctures its mouth with a jackknife to kill it. Struthers is left hanging upside down on a tree and is decapitated by the last crocodile, while James finishes the final threat with a series of explosives that destroy the crocodile’s nest.
In the end, Scott, Kerri, James, and Emma leave the lake together. Scott and Kerri are reunited with Daisy, who had become separated from them earlier, and the two share a kiss. James and Emma then carry the crocodile eggs they recovered to a laboratory for analysis, hoping to unlock answers about the nest and the species that terrorized the lake. The story closes with a quiet acknowledgment of the costs of survival and the fragile mysteries that still linger beneath the water’s surface.
