Over three months after blind, armor-plated extraterrestrial predators with hyper-sensitive hearing wipe out most of Earth's human population, the Abbott family scavenges medical supplies inside an abandoned town supermarket. The family consists of father Lee, pregnant mother Evelyn, deaf daughter Regan, son Marcus, and four-year-old Beau. Communicating solely through American Sign Language, they walk barefoot on hand-laid sand paths to muffle their footsteps. On their trek home, young Beau secretly turns on a noisy toy space shuttle he smuggled from the store. The sirens wail through the trees; despite Lee sprinting desperately to reach him, a creature streaks out from the woods and kills the boy instantly.
Over a year later, the family lives on an upstate New York farm, still shattered by grief. Lee spends his days in the basement trying to modify cochlear implants to restore Regan's hearing and attempting to establish radio contact with survivors, while Regan carries bitter guilt over giving Beau the toy's batteries. Evelyn is now in her final trimester of pregnancy, preparing an underground cellar equipped with oxygen masks, soundproofing, and a cushioned crib to muffle infant cries.
Lee takes Marcus to a roaring river waterfall to teach him to catch fish, demonstrating that small sounds are masked by continuous loud water. Marcus confesses that Regan believes Lee blames her for Beau's death and begs his father to tell her he loves her. Meanwhile, Regan visits Beau's roadside memorial alone.
Back at the farmhouse, Evelyn goes into early labor. Walking down to the basement, her foot snags on an upturned nail sticking out from the wooden stairs, causing her to drop a glass picture frame. The crash alerts a nearby creature, which enters the house. With contractions escalating, Evelyn turns the outdoor string lights to red—the emergency alert code—and retreats to the bathtub, struggling to hold back agonizing screams as the monster stalks into the room.
Lee and Marcus return to see the red lights. Lee instructs Marcus to set off fireworks in the fields to create a loud acoustic distraction. Just as the fireworks explode, Evelyn unleashes a muffled scream, giving birth safely to a baby boy. Lee rescues Evelyn and hides her in the soundproof cellar before going out into the fields to search for Marcus and Regan, who have taken shelter atop a tall grain silo.
At the silo, the roof hatch gives way, plunging Marcus into the corn below. Regan jumps in to save him, but the shifting grain nearly suffocates them before a creature stalks onto the silo floor. Regan's malfunctioning cochlear implant suddenly emits a piercing, high-frequency feedback screech that disorients the monster, causing it to tear through the metal siding and flee.
Lee finds the children near his pickup truck, but an alien ambushes them, severely slashing Lee's chest. Marcus screams, alerting the beast to the truck where the kids are trapped inside. Looking at his daughter, Lee signs "I have always loved you" before unleashing a full-throated roar, drawing the beast toward him and sacrificing his life so Marcus and Regan can coast the truck safely down the hill back to the farmhouse.
