Two years after a satanic cult led by his former babysitter Bee tried to kill him, Cole is now a junior in high school. He is unable to convince anyone, except for his best friend Melanie, of Bee’s life-threatening plot; his parents and most others think he had a psychotic break. He discovers that his parents have enrolled him in a psychiatric school, and he escapes with Melanie alongside her new boyfriend Jimmy, and their friends Boom-Boom and Diego to join a lake party.
At the party, Cole witnesses the arrival of new student Phoebe at the lake after finding a stuffed toy and directions to the lake. Later, Cole’s friends play a party game on a boat when Melanie suddenly kills Boom-Boom with a boathook and saves her blood. Melanie, Jimmy and Diego are revealed as cult members. With Boom-Boom’s blood as a sacrifice, they need Cole’s blood as an offering of an “innocent” to make their wishes come true. Original cultists Sonya, Allison, Max, and John also appear, having been resurrected so they could partake in the ritual by sunrise. However, Phoebe suddenly appears, looking for gas for her jet ski, and provides Cole with some time to evade the cult members and escape with Phoebe on her jet ski.
Once on land, Cole explains everything to Phoebe, who believes him, while the cultists give chase. Sonya makes the first attempt to kill them, but they end up running her over with a car left by a stranger and decapitate her with a surfboard. Allison finds them, but the two trap her between a narrow wedge of rocks and rip her head off. The two board a boat and drive off, but Max catches the raft attached to the back of the boat and is able to pull himself onto the boat. However, Phoebe sets him on fire with a can of silly string and a lighter, then shreds him with the boat’s propellor. Diego and Jimmy supernaturally disintegrate when they attempt to back off from their pursuit of Cole.
Cole and Phoebe arrive at Phoebe’s old family cabin, where they take refuge and hope to wait out the night. In the cabin bunker, Phoebe reveals to Cole that her parents died because she crashed into them in a fatal car accident. Cole comforts her, and the two have sex. Melanie calls Cole’s father Archie, who has been searching for him alongside Melanie’s father Juan, and fakes being drunk so that he can pick them up, hoping to lure Cole out. Cole and Phoebe come out of the bunker armed with crossbows and John accidentally kills himself when a chandelier crashes on him. Archie gives Cole a sleeping drug so he can take him to his car as Melanie kills Juan with a machete and captures Phoebe.
While stopping for gas, Cole regains consciousness, locks Archie out of the car, and drives back to the lake to save Phoebe. In a cove, Melanie holds Phoebe hostage before Cole shows up and volunteers to be sacrificed. Bee emerges from the water and is revealed to be Phoebe’s babysitter who was responsible for the car accident that killed her parents. She made a deal with the devil to save Phoebe’s life in exchange for her soul. Sonya, Allison, Max, and John are resurrected again, and the four alongside Melanie drink the blood of Cole mixed with Boom-Boom’s blood. However, since Cole has had sex with Phoebe, the ritual backfires and the five melt and disintegrate. Max is proud of Cole, while John tries to accept Jesus Christ as his savior before dying. Bee, who did not drink the blood, reveals that she orchestrated everything so that Phoebe and Cole could unite and defeat the cult, having had a change of heart after Cole’s love confession after her initial defeat. However, since Bee is still technically a demon, she drinks the blood and disintegrates to save the two. Archie shows up and, having witnessed Bee’s death, now believes what Cole said was true. As the sun comes up, Cole and Phoebe embrace in a kiss, while Archie looks on proudly.