In 1972, a young camper at Camp Whispering Lake tries to locate his missing peers, but fear drives him deeper into the woods. He stumbles upon an abandoned cabin and hides from an unseen force as the night closes in. When the police arrive later, they find the campsite deserted—every camper has vanished without a trace.
In the present, the two brothers, Dylan and Dane, are being sent to a military-style camp after a reckless act: they set their house on fire with a rocket bought on their mother’s credit card. During pickup, they manipulate two camp counselors from Camp Bushwhack into taking their places at the boot camp, and the brothers slip away to Camp Bushwack under the identities of Sanjay and Delroy. Upon arrival, the boys discover they’ve been dropped into a troubled, even chaotic, cabin environment, and a budding rivalry erupts between Brogan and Dane as he clashes with a rival cabin counselor.
To settle the score with Brogan, the brothers and their bunkmates hide Brogan’s trophy, the Nameless Cup, in an old cabin. There, they uncover a creepy old backpack containing a book full of scary stories. Unbeknownst to them, that same cabin is the very one the 1972 camper used to hide from danger. As the night unfolds, the boys decide to tell those stories around the campfire, and a tale about Anson Miner—a former Camp Whispering Lake counselor—begins to blur the line between fiction and reality. In the story, Anson drowns, is revived by a doctor, and returns as a brain-eating zombie who kills the doctor; the zombie infection spreads, but the group is briefly cured until they learn that Anson’s undead state makes the antidote ineffective.
The next day, strange signs appear. A counselor named Lauren grows a mustache, echoing the stories told at the campfire, and Dylan catches a glimpse of Anson prowling the woods. He goes to the camp manager, Crawl, to ask about the no-telling-scary-stories rule. Crawl reveals that Camp Bushwhack used to be Camp Whispering Lake, and that a long-ago disappearance prompted the strict policy against scary tales—almost certainly because the book in the cabin is tied to those vanished campers. Dylan attempts to warn everyone at the next campfire, but the warning falls on deaf ears. On a hike, Dane refuses to believe him until he’s attacked by Anson, forcing him to accept the danger.
As the stories begin to come true, the trio and their cabinmates race to the animal hospital to shelter from Anson. They equip Anson with a remote-controlled collar intended to restore his pre-zombie personality rather than undo his undead state. The plan buys them time, but it backfires when Brogan, hunting for the Nameless Cup in the hospital, confronts Anson and shatters the remote, restoring Anson to his zombie form. Back at camp, Brogan and Anson, now both bitten, attack the others. The group fights to drive off the zombies, while Dane admits he was scratched and Dylan searches for any remaining campers. He and Dane manage to locate Lauren and send two captives—Genius Bar and Grinsberg—back to the hospital to seek the antidote. They are aided by the return of the real Sanjay and Delroy, who had escaped the boot camp.
With the antidote freshly produced by Genius Bar, the brothers work to cure the zombie-turned campers. Dane briefly becomes a zombie again but is quickly cured, and the camp celebrates with a Hawaiian party. In the final moment, the book is burned to put an end to the curse, but the ending hints at trouble still to come: counselor Alice reads aloud all the stories in the book by accident, including one about a shark in the lake, suggesting a looming threat for future campers.
