Short answers, pulled from the story.
David Drayton and his son Billy become trapped inside a local supermarket in Bridgton, Maine after an unnaturally thick mist envelops the town following a severe thunderstorm. The mist conceals strange and hostile creatures, transforming their routine grocery run into a fight for survival while an earthquake damages communications and cuts off hope of immediate rescue.
Mrs. Carmody is a religious fanatic who convinces the group of survivors that the events are a biblical prophecy of the end times requiring human sacrifice to save them from God's wrath. She attempts to offer Billy and Amanda as sacrifices when the survivors try to escape to David's car, but Ollie shoots and kills her before her congregation dissolves in confusion.
The Arrowhead Project is a rumored scientific experiment conducted at a nearby military base where scientists look for portals to other worlds and dimensions. Two soldiers from the base commit suicide in the store's stockroom, suggesting they discovered something too terrible to live with and hinting at the potential dangers of the project.
The film adaptation directed by Frank Darabont alters the ending so that after running out of fuel, the survivors agree to commit suicide, with David Drayton killing the others including his son before the mist begins to disperse. A US Army convoy then approaches to destroy the remaining creatures and assist survivors, revealing they were only moments from rescue.
Mindscape released an interactive fiction computer game based on the novella in 1985, and ZBS Productions released a full-cast radio drama in 3-D Sound in 1986. A television series based on the novella's premise aired on Spike in 2017 and was cancelled on the 27th of September 2017 after just one season.