Emily and Randall arrive at Randall's parents' beach house in a remote vacation town, a place that looks quiet and deserted as the sea air brushes the windows. They are soon joined by Mitch Mitch and Jane Turner, old friends of Randall's father, who are also staying there for what Jane hopes will be a last, peaceful getaway for her. The two couples settle in, drawn together by space and shared company, and the mood shifts from relaxed to wary as a quiet tension threads through the evening.
After dinner, Randall proposes that everyone share some edible marijuana he brought along, and Jane and Mitch agree to join in. As the high settles in, Mitch notices something unusual in the water—the texture of the surf and the water itself looks almost animated, and glowing microbes seem to cling to the beach and the trees in a startling display. Jane slips away to get a closer look but begins coughing and grows disoriented as a dense fog begins to creep over the area. When the fog thickens, Emily too loses her bearings and slips into unconsciousness.
Emily wakes to a scene she never expected: Jane sits in the kitchen, catatonic and covered in skin lesions, while Mitch is missing. The house feels heavier, and the air seems to vibrate with a low, uneasy hum. The next morning, they step outside and discover the beach is utterly empty, as if the town itself has exhaled and vanished. Randall grows pale and sick at once, rushing back indoors, where the sink water churns with strange patterns, and a moan from Jane makes him hurry toward her side. On the shore, Mitch reappears, oddly calm yet off, confessing that something about the place feels wrong before he heads toward the water and drowns himself.
Emily, in a scramble to stay alive, steps on a washed-up Portuguese man o’ war and experiences a searing sting and a glimpse of a worm-like creature wriggling under her skin. She fights back the panic and crawls back to the house, where she finds Randall already in trouble, pursued by Jane, whose eyes have turned milky and whose mouth leaks a strange fluid. She locks Jane away, and the two of them flee into the fog that continues to thicken the night.
The fog blankets the area, and Randall’s condition worsens rapidly. In a desperate bid for information and safety, Emily discovers a police car with a radio in it and reaches out across the radio’s crackling channel to connect with someone who can help. A voice on the other end asks if they have been exposed and urges them to barricade themselves and avoid breathing in the fog until help can arrive. The situation grows more dire as they take shelter in another home, discovering that the water around them has shifted into an entirely different texture and color.
Emily turns on the television and finds an Emergency Alert System blasting across every channel, followed by a radio broadcast explaining that the microbes—once preserved in underwater rocks—were released due to global warming. The report suggests that they have to endure the morning, but Randall is certain they will not make it through the night. Determined to survive, Emily makes a move into the basement where she uncovers scuba diving oxygen tanks that she believes can provide clean air, a critical lifeline in this suffocating fog. In the same basement, she encounters a horrifying mutation—a person altered by the contagion, feeding on a corpse, a grotesque warning of what could come.
Upstairs, Randall vomits a squid-like creature, and his eyes turn white as the infection takes its final hold. In a tense moment of survival, Emily returns with the scuba gear and uses force to subdue Randall when he lunges toward her, knocking him unconscious with a scuba tank. She gathers the car keys, climbs behind the wheel, and drives away, only to crash into a tree as the fog disorients her. She staggers from the wreck and stumbles into a tide pool, where she lies, breathing in the fog and letting her mind drift through hallucinations of the microbes in the water.
Dawn arrives with a heavy gray light, and Emily lies on the shore, trying to steady her thoughts as the infection seems to reach its final phase. She clings to a stubborn resolve not to surrender to fear, even as a wave approaches and drags her out toward the open sea. The sea consumes her breath as the fog Internet of horror continues to close in, leaving the outcome uncertain and the memory of the town’s eerie quiet echoing long after the sun has risen.
