Trama

A severe thunderstorm strikes Bridgton, Maine, causing a tree to fall into the lakeside home of artist David Drayton, his wife Stephanie, and their eight-year-old son Billy. While surveying the damage the next morning, they notice a thick mist advancing over the lake. David and Billy leave for the town with their neighbor Brent Norton to buy supplies.

From inside the supermarket, they watch police cars speed down the street. A terrified local, Dan Miller, runs into the store and warns of a danger lurking in the mist. As a civil alert siren sounds, store managers Ollie Weeks and Bud Brown close off the supermarket, and the mist envelops the store. One woman leaves to go home to her children.

Against David's advice, bagger Norm starts to go outside to fix the store's emergency generator, but he is grabbed by a tentacled creature and dragged into the mist. David and Ollie direct the customers to barricade the storefront windows. Mrs. Carmody, a religious fanatic, begins preaching about an impending Armageddon. Brent disbelieves the dangers of the mist and leaves the store with a small group to seek outside help. His group is attacked by an unseen force and presumably killed.

David forms connections with several people in the store, including Amanda Dunfrey and Irene Reppler, two teachers who came into conflict with Carmody over her religious take on the ongoing disaster. Amanda carries a revolver in her purse and gives it to Ollie, who is a former regional shooting champion. As night falls, enormous flying insects, attracted to the lights, swarm to the store windows and are preyed on by pterodactyl-like creatures. One of the predators (Including big locusts) smashes a window, allowing both species inside. In the ensuing panic, two people are killed while another receives fatal burns while attempting to incinerate the insects. Meanwhile, Carmody is miraculously spared from an insect, which convinces her to proselytize more fervently and gain followers among the survivors.

A small group led by David goes to the neighboring pharmacy in search of medical supplies but is attacked by giant spiders that kill two men, forcing them to retreat. Carmody, who had opposed the expedition, uses this failure to increase her influence by offering protection from divine wrath to new converts.

The next day, following the suicides of two soldiers from the local military base, a third soldier, Jessup, reveals that a government project to discover other dimensions was underway at the base and that scientists accidentally opened a doorway into the creatures' habitat. Angered and vengeful, Carmody's followers offer Jessup as a sacrifice and expel him from the supermarket. Outside, he is immediately devoured by a giant praying mantis-like creature.

As David and his group prepare to leave the store the next morning, they are stopped by Carmody. Billy has been chosen by her group to be delivered as the next sacrifice to appease the monsters. As the crowd descends on Amanda and Billy, Ollie shoots and kills Carmody. The traumatized survivors then allow the group to leave. As the group makes its way through the parking lot, Ollie is devoured by the praying-mantis like creature, while two others Myron and Ambrose are killed by the spider-creatures from the pharmacy. Bud runs back to the store and is let inside by the patrons. David, Billy, Dan, Amanda, and Irene reach David's car and leave.

Driving through the mist, David finds his home destroyed and Stephanie dead. Devastated, he drives away from town, passing a colossal six-legged beast and eventually running out of gas. With no means of escaping the mist, the adults decide to end their lives. Aiding their suicide, David shoots Billy and the other three survivors with his four remaining bullets before leaving the car to be taken by the creatures. The mist suddenly dissipates, revealing the vanguard of a U.S. Army armored column beginning the process of exterminating the creatures and restoring order. David, seeing that the Army has also rescued survivors, including the woman who left to get to her children, realizes that he killed his son and fellow survivors as they were just moments away from rescue. He drops to his knees, screaming in despair.