After a violent thunderstorm damages their Maine home, artist David Drayton and his young son Billy head to the local supermarket to gather supplies. Soon after they arrive, an ominous mist rolls over the town, bringing with it an inexplicable sense of dread. The townspeople quickly find themselves trapped inside the supermarket, cut off from the rest of the world by the thick, foreboding fog. Amidst the confusion and rising panic, the patrons soon realize that the mist conceals otherworldly creatures that pose a grave threat to anyone who dares venture outside.

The group inside the supermarket is a microcosm of society, featuring a diverse range of personalities and backgrounds, which causes tensions to soar as the situation worsens. Fear and paranoia lead to the fracturing of the group, with some rallying behind a level-headed attempt to understand and face the mysterious threat, while others fall under the sway of Mrs. Carmody, a fanatical woman who believes the mist is a divine punishment. This ideological divide breeds mistrust and conflict within the increasingly claustrophobic confines of their makeshift refuge, as the true nature of the mist and its terrifying inhabitants becomes ever more clear.