It's another day in the life of Lieutenant Frank Drebin of Police Squad. Drebin is coming back from battling Mexican drug dealers, unaware that something is watching him. After being congratulated on yet another job well done, Drebin returns home for a night of love with his wife, Jane Drebin. The following morning, Frank gets a call from Ed Hocken that there was a brutal murder in the harbor area of Los Angeles. Frank heads out and meets up with Hocken and Officer Nordberg.
The officers enter a warehouse and find the skinned bodies of three security officers hanging from a pipe by their ankles. The officers don't find any evidence of the culprit, but they do find evidence of a struggle, as several crates are shown to have bullet holes and blood stains on them. One crate, however, is shown to have been blown apart, and a green liquid is seen dripping from a stair.
While the bodies are loaded into a truck to be taken to the morgue, an analysis shows that the green liquid is actually blood. Frank jokingly states that whoever committed the murders "must not have had alot of iron in their diet", a joke everybody in the lab laughs at. Just then, a report comes in that suspects have been apprehended. During the interrogations, however, each suspect claims they had nothing to do with the skinning of the three security officers. With no leads, Drebin decides he needs to go back to square one.
Drebin returns to the crime scene and looks around for anymore clues as to who committed the murders. Just then, Drebin spots somebody walking out of the warehouse and proceeds to chase the person down. He then tackles the person and proceeds to angrily question him, only to be grazed by a laser beam. He gets up and sees a set of yellow eyes, which quickly disappears. Drebin then proceeds to fire his pistol wildly, only to hit nothing.
Drebin then returns to the lab and reports that the killer is an invisible force. The other officers laugh this off, and Drebin goes back and attempts to call out to the invisible figure, but to no avail. Just then, Hocken and Nordberg pull in, offering to help Drebin find the murderer. Just then, Hocken and Nordberg's patrol car blows up, and the trio point their guns in the direction of the rooftop, and something invisible drops down to the ground, and a set of blades appears and stabs into Nordberg's abdomen. Hocken fires wildly toward where the blades are at, only to find his spine and head being yanked out by the unseen force. Before Drebin can open fire, Nordberg's body is dragged away by the unseen force.
Drebin, now more determined than ever to stop the perpetrator, returns to the station and collects several weapons, including a rocket launcher and a minigun. He then dresses up to look like Rambo and returns to the streets to confront the invisible murderer. Drebin angrily calls out to the murderer, and something invisible drops, and then, the invisible figure turns visible, revealing a 7-foot tall reptile-like humanoid figure with a shoulder cannon, dreadlocks, fishnet clothing, wrist gauntlets, and a metal mask. The figure then removes it's mask, revealing a grotesque face, consisting of a small mouth with four crustacean-like mandibles around it.
Drebin resists vomiting at the sight of the creature's face, and proceeds to assault the creature as Judas Priest's "No Surrender" somehow plays in the background. Neither combatant is able to best the other, and at least four buildings are destroyed in the fight. Eventually, Drebin wounds the creature with the minigun. Collapsed, and at Drebin's mercy, the creature opens one of it's wrist gauntlets, and strange symbols appear on small screens on it. Drebin, realizing it must be a self-destruct sequence, runs off. He goes to set off a tornado siren, and the people of the city flee, with Drebin not far behind.
Once everybody is out of the city, the self-destruct countdown finishes, and the city is incinerated in the explosion. Drebin laments at the loss of several years of police work, but is hailed as a hero by the city.
Alternate Ending:
After being wounded by Drebin, the creature succumbs to it's injuries and dies. Just then, several more creatures like it appear and, despite Drebin's expectations, they collect the other creature's body, and one of them, a pale-looking one, pulls out a Native American tomahawk and tosses it to Drebin. The creatures then turn invisible and head to what appears to be an alien spaceship, which they enter as it flies off into the night.