Humongous

In 1946, Ida Parsons is chased into the woods and raped by a houseguest. Ida’s dogs break free and attack the attacker, killing him. The brutal incident seeds Ida's paranoia and her lifelong distrust of outsiders.

In 1982, brothers Eric and Nick borrow their father’s yacht to take their girlfriends, Sandy and Donna, and their sister Carla on a weekend trip to St. Martin Island. They encounter a shipwrecked fisherman named Bert, whom they rescue. Bert regales them with a campfire story about wild dogs that allegedly roam Ida Parsons’ island.

Ida Parsons has spent thirty-five years holed up on Dog Island, using her fortune to keep herself secluded. She makes only two supply runs to the mainland each year and refuses to engage with anyone. Her isolated life sets the stage for the island’s deadly legends to feel real.

Their boat wrecks, and the group washes up on Dog Island. Bert is wounded, Carla is missing, and Nick wanders into the woods where he is killed by a hulking figure. The island’s dangers become immediately personal as the survivors realize they are not alone.

The next morning, Sandy and Eric go into the interior to seek Ida Parsons and plead for help returning to the mainland. They push toward Ida’s fortified residence while Bert, left behind, slips into shock from his injuries. The search marks the first direct confrontation with the island’s guardian secrets.

While the group splits to gather supplies, the hulking killer—the island’s elusive predator—surfaces again. Donna is hurled against a rock wall and Bert is decapitated, revealing the killer’s brutal mastery and leaving the survivors stunned. The violence confirms outsiders are under deadly threat on Ida’s island.

Eric and Sandy gain access to Ida’s fortified cabin and find all of Ida’s dogs dead, their skeletal remains scattered in the pens. They explore further and discover Carla hiding under a tarp in Ida’s boathouse. The grim scene hints at a hidden family legacy of violence.

In Ida’s house they uncover a dust-covered nursery filled with antique toys and a diary with rambling passages about birthing a sick child. The entries reveal Ida’s intention to keep her child sinless by isolating him from the world. These discoveries deepen the mystery of Ida’s past and its connection to the killings.

The group finds Ida’s skeletal corpse in her bedroom, confirming she is dead. Carla’s later survival hints that Ida’s son remains the mastermind behind the murders. Eric and Sandy begin to suspect a mutant son trained by isolation to hunt outsiders.

Eric and Sandy conclude that Ida’s 35-year-old mutant son—raised by isolation and driven by fear of outsiders—is the responsible killer. He has learned to survive through brutal hunting and has even eaten the dogs to sustain himself. The revelation heightens the urgency to escape.

The mutant attacks Ida’s house, breaking through the door. Eric fights with a broken branch, but the mutant fatally breaks his back, eliminating one of the last adults with a purpose. Sandy remains on the run, realizing the danger is not over.

Pursued to the boathouse, Carla is grabbed by the mutant and killed, sealing another life lost to the island’s horrors. The surviving trio braces for a final confrontation.

Sandy sets Ida’s boathouse on fire in an attempt to drive off the killer. The mutant presses the attack, burning and scarifying as it chases her. The fire provides a crucial distraction that enables Sandy to escape.

Sandy corners the mutant on a hill and uses a sharpened signpost to impale him, ending the immediate threat. She is left scarred by the violence she has witnessed and committed, a reflection of Ida’s own broken life. The island’s brutal history closes in on her as she sits on Ida’s dock.

In the aftermath, Sandy sits alone on Ida’s dock, visibly scarred by the killings and the fire. The survivors’ once-hopeful weekend has become a haunting memory of isolation and fear. The film ends with her solitary vigil, mirroring Ida’s lonely fate.