On his family’s lakeside lodge in northern Wisconsin, six-year-old Peter van Cleese witnesses a chilling event: his grandfather appears to be overtaken by a supernatural force as a reel-to-reel tape crackles and the man slips from the dock into the water, never to be recovered.
Seventeen years later, [Peter van Cleese] is a recent graduate who returns to the lodge with a close-knit group of friends — Ann Colbert, Kiersten Knudsen, Rodney, and Tom “Finner” Finnegan Finner — for a first visit since the disappearance. They are greeted by the wary local manager Wayne Duerst and his paranoid Vietnam veteran neighbor Evelyn Duerst, whose hostility foreshadows trouble to come as the town ramps up for its annual muskellunge fishing festival, “Muskie Madness.”
That evening, a middle-aged tourist named Shiela Swain is attacked on a nearby dock, ensnared by a heavy fishing line and dragged toward the lake. The following day, [Rodney] encounters Beverly Duerst — Bev D. — a local mother who helps organize the festival, and the group visits a fishing shop run by Leroy Leudke. Leudke shares a troubling recollection of how Peter’s grandfather and [Wayne Duerst] used to reel in trophy fish by pulling them to shore and shooting them, a practice they supposedly halted after Wayne accidentally shot Peter. Meanwhile, Peter grows increasingly unsettled by the very lake that inspired his grandfather’s mysterious fate, and [Ann Colbert] tries to comfort him, suggesting his distress might be post-traumatic.
Rodney takes a solo boat ride and is brutally attacked by an unseen assailant who castrates him with a large fishing hook before dragging him under. The police recover a blood-soaked, empty boat, while Peter accuses [Wayne Duerst], though the local sheriff works to suppress the investigation to avoid disrupting the festival. A distraught Kiersten swims to rest, only to be struck by a looming, oversized hook. In parallel, [Finner] and Beverly find time to grow closer.
That night, as locals host the contest for the biggest muskellunge, Denny Dobyns is stranded when his boat’s motor fails. He signals for help, but a fish-hook attack closes in on him and pulls him under the water. Beverly disappears after a short swim, attacking the same way as the others. Peter and Ann search for Kiersten, while a distraught Evelyn confronts them with the grim news that Bev is missing. An intoxicated [Finner] takes a boat out, blasting music from a boombox, and the racket — amplified by cicadas’ chirps — unsettles the nearby hardware owner [Leroy Leudke], who has a head implant from a Korean War injury. In a fury, Leudke hurls a fishing hook at Finner, tearing off his ear, and then dismembers him, grinding the remains into fishing bait.
Kiersten finally returns to the lodge, telling Peter of a harrowing encounter with a large fishing hook and how she escaped by swimming to the far shore before losing her way in the woods. A music student, Peter reasons that the combination of cicada chorus and certain musical notes can yield the “Devil’s tritone,” a frequency capable of driving some people mad. Evelyn suggests that Leudke’s metal plate in his head could amplify these sounds to dangerous levels. The duo investigate Leudke’s shack and uncover jars of human organs, a horrifying discovery that confirms the worst fears.
As Peter and Evelyn hurry back to the lodge, Ann is abducted by Leudke and imprisoned in his bait shop refrigerator. [Wayne Duerst], along with Evelyn and Peter, joins the effort to stop Leudke. At the next dawn’s festival, Leudke unexpectedly wins the contest, and Wayne publicly accuses him of murder, though the sheriff remains unconvinced. That night, Peter confronts Leudke in his shack, wounding him with a treble-hook, but Leudke retaliates and overwhelms Peter. Peter regains consciousness to free Ann, and Leudke flees as police sirens approach.
Dawn finds Peter, Ann, and Kiersten leaving town, while [Wayne Duerst] and the sheriff search the surrounding woods for Leudke, convinced he won’t get far. The sheriff suspects that Leudke will die from blood loss due to the injury left behind, leaving the lodge’s dark, waterborne mysteries unresolved but finally relegated to the town’s collective memory. In the end, the lake is left with a heavy, haunted quiet, hinting that something otherworldly may still linger beneath its surface.
