Belief divides them, mystery surrounds Them, but fear changes everything
Why it is hard sci-fi
A small town is enveloped by a fog containing organisms from a different physical environment. The cause, the Arrowhead Project, is a military experiment that has opened a connection to another dimension. The film is precise about the local logistics. A small crowd in a supermarket, dwindling supplies, and a pharmacy run that is literally a casualty count. The science is bracketed but the procedural texture is documentary.
Science inside it
Inter-dimensional aperture as a research-program failure, alien biology adapted to a different physical environment, and the social dynamics of a small group under siege. The films engineering interest is in what a half-day of community failure looks like.
Spoiler alert
The protagonist shoots his own son and the other survivors to spare them the creatures, then steps out of the car and finds that the military has already cleared the mist on that road minutes earlier. The films thesis is that a wrong decision under uncertainty is permanent, and it commits to the consequence in the last minute of runtime.