A subterranean race of reptile-men, nicknamed the slime people for their slime-covered skin, emerge from the depths after underground atomic tests force them from their lairs and set their sights on Los Angeles. They unleash a strange, organic-looking machine that generates a wall of “solidified fog” around the city, turning the urban landscape into a hazy, perilous trap. The invasion follows the aliens’ exile and their need to operate in conditions that the fog enables, gradually isolating the metropolis and pushing the surface into a state where life becomes a constant fight for survival.
Tom Gregory, Robert Hutton, a pilot who has just weathered flight trouble, lands in a city that feels almost abandoned. He moves through empty streets and silent neighborhoods, wary of what might be lurking behind the fog and the quiet. His arrival is a catalyst for the fragile group of survivors who begin to form a plan: a Marine separated from his unit, and a scientist with his two daughters, trying to make sense of the crisis and protect those who manage to cling to hope.
Prof. Galbraith, Robert Burton, is a key figure in the effort to understand the invaders and their peculiar biology. With him are two young women who belong to his family circle—Lisa Galbraith, Susan Hart, and Bonnie Galbraith, Judee Morton—whose courage and resourcefulness become crucial as the fog closes in and the city’s defenses crumble. The group realizes that the slime people are largely immune to conventional weapons because their bodies heal rapidly, sealing wounds almost as quickly as they are made. Yet the aliens have a vulnerability: the spear-like weapons they wield are hollow, and wounds inflicted by them prevent the breath from closing properly, offering a potential route to neutralize the threat.
Amid the tense search for safety, a KTTV reporter named Vince Williams, John Close, documents the chaos and serves as a reminder of the outside world watching Los Angeles struggle to survive inside the fog. The survivors come to understand that the fog is not just a shield for the slime people; it also cools the surface to permit activity around the clock, giving the invaders an unsettling clockwork advantage that makes every minute count.
As the group pieces together the puzzle, they uncover a crucial detail about the fog’s origin: the plane that first landed within the opening siege wasn’t merely lucky—its landing was aided by a chemical reaction between the fog and salt from sea water, which prevented the sea-side section from solidifying. This discovery reframes the crisis, offering a glimmer of possibility despite the ever-tightening noose of the fog.
With this knowledge, the survivors attempt a bold plan to breach the barrier. They gather saltwater solution and hope to carve a hole through the wall by leeching a channel of liquid through the fog, allowing an escape route and a chance for reinforcements to enter. The effort is desperate and perilous, because they are short on the solution and time is running out. When that plan falters, they pivot to their next option: destroy the machine that generates the fog. The act is fraught with risk, as the device seems to be the heart of the invasion—its collapse would spell the immediate dispersal of the fog but also unleash a frenzied counterattack from the slime people.
The machine is ultimately toppled, and the fog dissipates rapidly. With the veil lifted, the military is able to sweep into the city, and the slime creatures begin to succumb to the dramatic shift in conditions—the temperature spike that follows the fog’s collapse proves lethal to them, and they die off as the city reclaims its ground.
In the aftermath, the remaining survivors confront the heavy price of their endurance and the collective effort it took to survive a crisis that blended science fiction with survival drama. The film closes on a note that underscores human resilience: even when the odds seem insurmountable, quick thinking, collaboration, and a willingness to take calculated risks can tilt the balance between annihilation and survival. The story is told with a restrained, observational tone that emphasizes the human dimension—the fear, the hope, and the stubborn will to endure when a city is threatened from below and from beyond.
