A couple on a quiet sail reaches a secluded island, and the woman wanders ashore to explore a fenced-off, seemingly abandoned compound. The moment feels tense and uncertain, as if the place itself holds a warning. She is soon confronted by something unseen, and the encounter ends with an attack that hints at a threat far more dangerous than it first appeared.
Later, two brothers, Matt and John, fly in on a seaplane for a week of rest on the same island. The uninhabited land was once owned by their late uncle, who built a cabin there, and they are joined by three friends: Nicki, Sara, and Noah. They quickly settle into a rough, sun-dappled routine, until a stray puppy appears and growls at Noah before darting out of the cabin. John and Sara follow, only to be ambushed by an older, vicious dog that sinks its teeth into Sara, turning a tranquil excursion into a dangerous scramble for safety.
The next morning, the group treks into the forest and encounters the blood-soaked man from the island’s opening scene, now a harrowing messenger clutching a warning about the dogs. He is killed by a pack that swarms him, forcing the friends back toward the cabin where the threat feels suddenly intimate. Nicki is targeted in the ensuing assault, and John’s aim misfires—an arrow intended for a dog tears into Nicki’s calf instead. As more canines press their attack, one dog is driven off with a fire iron but the danger only grows, and the house becomes a siege.
With no clear escape and the dogs closing in, the friends decide they must leave the island. Yet the seaplane is compromised: the dogs have surrounded the craft, gnawed through the mooring ropes, and sent it drifting away from reach. John makes a desperate attempt to reach the plane, swimming through a sea of barking, snapping dogs to reach the dock. Meanwhile, the others retreat back to the house, where Sara begins to display increasingly animal-like behavior, a sign that the threat might be more than mere wildlife.
Seeking a way out, they head to a storage shed and grab their uncle’s Mercedes-Benz, intending to drive to a nearby training complex to contact help. The car stubbornly won’t start, leaving them stranded as a power outage plunges the house into darkness. Noah heads down to the basement fuse box and is killed by dogs that have slipped inside. Matt is bitten next, and the trio takes shelter in the attic, where they uncover papers linking the place to a training program. It becomes clear this was an Army facility designed to train attack dogs, a revelation that alters everything they thought they knew about the threat they’re facing.
When dawn arrives, the dogs seem to have withdrawn. The survivors make a failed attempt to restart the Mercedes and leave, but Sara hesitates and is again attacked, tumbling from a window and impaling both herself and a dog on a nearby post. The shock of her death steels the others for what comes next, and they press on toward the abandoned facility that holds the key to understanding the dogs’ true nature.
Inside the facility, they discover that the dogs have been genetically enhanced. John locates communications gear, but an antenna cable has been deliberately unplugged, blocking any easy call for help. Matt, already bitten, discovers a terrifying new trait: he can sense the dogs and realizes that if they manage to escape again, they could return in force. John works to repair the antenna but is struck by an electric shock, collapsing as the dogs close in. Matt arrives brandishing a baseball bat, fighting the pack, but a power surge triggers a deadly backdraft that rips through the building. In a last-ditch move, Nicki lures the dogs into the collapsing structure, and the blast and ensuing fire consume the dogs inside.
John reveals that he spotted a nearby boat belonging to the couple from the island’s opening scenes. The dogs close in on the brothers but appear momentarily docile as Nicki returns in the Mercedes to haul them to safety. The car is overwhelmed by the dogs, forcing Nicki to drive it off the pier and into the water. They swim to the boat and set sail, aiming for medical facilities before Matt and John succumb to their injuries and turn feral like the dogs they’ve faced. The final image lingers on the cabin’s sleeping quarters—a stowaway dog suddenly surging from the shadows, suggesting that the threat may not be extinguished after all.
