Three beings, disguised as human males wearing leather jackets, are part of an advanced alien invasion force sent to Earth to infect city water reservoirs with a bacteria that will kill all humans and domestic animals. Their motivation is to colonize Earth for their own race to expand, and since humans are violent and hateful they deserve to be destroyed. Calling themselves "Scott", "Steve" and "Fred", they rent a house in a suburban American town where they keep in contact with their planet's ruler.
Unexpectedly, Scott — the youngest of the three aliens — falls in love with Ellen Tillman, a girl who lives next to their rented house. Scott eventually tells Ellen about the alien plan and tries to convince her to run away with him, but Ellen naturally mistakes his story for lunacy. Ellen's father contacts the local sheriff to take Scott away, but unknown to him, the deputy who answers the call is part of the alien invasion.
Meanwhile, Scott contacts the leader of his world in an attempt to stop the extermination. Assuming the reports describing humans as inherently violent were made in error, Scott explains that while violent individuals exist, as in all races, the majority of humans are essentially loving and peaceful. The leader refuses the request and deems Scott a traitor. In a final attempt to save her, Scott returns to Ellen's house, but the "deputy" is there and takes him away. The Tillmans comfort their distraught daughter, none of them realizing they are doomed by the impending alien attack.
Black Leather Tropes:
- Cassandra Truth: Scott, who tells Ellen the truth about the alien attack, but is dismissed as a lunatic.
- Girl Next Door: Ellen Tillman is a nice, sweet girl who lives next door to the house that the aliens have rented. Scott soon falls in love with her.
- Greaser Delinquents: The aliens disguise themselves as this.
- Hell-Bent for Leather: The aliens wear black leather jackets as part of their disguise.
- Humans Are Bastards: The aliens justify their genocide of humanity this way.
- Hypnotic Eyes: Steve uses his eyes to hypnotize Stuart Tillman into thinking that he, Scott and Fred are nice young men, though the effect is short-lived.
- Interspecies Romance: The alien Scott falls in love with the human girl Ellen.
- Love Redeems: Scott loses his will with the alien attack once he falls in love with Ellen.
- Mind over Matter: Scott, Steve and Fred have telekinetic powers.
- Sarcastic Confession: Scott and Steve tell Stuart Tillman that they are monsters from outer space in a sarcastic tone when he asks them if they are ham radio operators.
- Shout-Out: Stuart and Martha Tillman are watching the game show To Tell the Truth when the signal cuts out due to the aliens' transmissions next door.
- Totally Radical: The aliens' use of teen slang is a gas, man. Dig it.
- Take Me to Your Leader: Fred asks Stuart Tillman to take him, Scott and Steve to his leader.
- Tuckerization: Scott, Steve and Fred are named after Earl Hamner, Jr.'s son Scott and two of his friends.
- Water Source Tampering: The aliens plan to exterminate humanity by contaminating water reservoirs all over the world with deadly bacteria. Thousands of advance troops have been sent to Earth for that purpose. Steve reports to their leader that every living thing in the state will be dead within 48 hours.