In the depths of Pennsylvania's Appalachian Trail, a group of cavers accidentally uncovers a vast underground chamber teeming with prehistoric bats. As the chaos unfolds, these blind bats, later dubbed 'vesps,' are irresistibly drawn to sound, leading to an epidemic of terror across the nation. In Montclair, N.J., just 20 miles northwest of NYC, Hugh Andrews, alongside his wife Kelly, their deaf daughter Ally, younger son Jude, and Kelly's mother Lynn, scramble to understand the gravity of the crisis as they watch a news broadcast warning them about the deadly vesps.
To escape the onslaught, the family and Glenn—Hugh's lifelong friend—decide to hit the road with Ally's dog, Otis. Amid their journey, Ally manages to FaceTime her crush, Rob—whose situation rapidly deteriorates as the crisis escalates. Their trek takes a dark turn when Glenn bravely confronts an armed assailant during a gas station stop, creating chaos as he shoots the man in an act of defense.
As they navigate overwhelming obstacles, a traffic jam forces them off-road, leading to a near-fatal accident for Glenn. He becomes ensnared in the wreckage, urging Hugh to escape without him as the swarming vesps close in. In a desperate act to save his family, Hugh has to release Otis, whose barking only attracts more danger. When the tension escalates, Lynn’s coughing summons one of the vesps, prompting Hugh to take drastic measures by igniting Glenn's overturned vehicle to divert the creatures.
With their vehicle rendered useless, the family embarks on foot into a nearby forest, ultimately discovering a fenced cabin. However, tragedy strikes when the vesps claim the life of the elderly owner, who attempts to scare them away with a shotgun. The family crawls through a drain to evade the threat but soon faces another harrowing encounter when a rattlesnake draws the vesps toward them, injuring Kelly.
Inside the cabin, they tend to Kelly's injuries while Ally reaches out to Rob for updates, only to learn his situation is worsening. Faced with the urgency of Kelly's infection, Hugh and Ally set out for medical supplies. During their exploration, they encounter a mysterious man known as The Reverend, who invites them to join his disturbing cult, The Hushed. Though they refuse, the threat of his intentions lingers.
As the family discovers the vesps' aversion to extreme cold, Ally becomes aware of a potential haven to the north known as The Refuge. Their hope is soon clouded when The Reverend, now with his followers, confronts them again, suggesting dark intentions for Ally's future. The conflict escalates as a girl associated with The Hushed unwittingly leads a vesp attack on the cabin, forcing the family into a life-or-death struggle.
In a pivotal moment of sacrifice, Lynn draws the vesps away, allowing Ally to escape while confronting tremendous danger. As Hugh and Kelly fight back, they ultimately confront and defeat The Reverend in a last-ditch effort to protect their family. The harrowing journey culminates with Hugh, Kelly, Ally, and Jude trekking north, where they finally reach The Refuge. Reunited with Rob, Ally embarks on a new chapter in survival, honing their skills and fending off the relentless vesps in a fight for their lives against the backdrop of a world turned upside down.
