The story takes place in Los Angeles in 1991. Three years prior an alien craft crash-landed on Earth. The saucer housed 300,000 "Newcomers", an extraterrestrial race of hard labor workers. With no way to return to their home planet, the Newcomers were first quarantined and then finally released to live among humans in the LA area.
An LA police detective, Matthew Sykes, and his partner, Detective Tuggle, are patrolling an LA Newcomer neighborhood when they spot two of the aliens dressed in long black coats entering a small convenience store. The aliens pull out shotguns and rob the store's owner. Sykes and Tuggle intervene when the robbers emerge from the store and a gunfight ensues. One of the newcomers changes the magazine on his shotgun and begins to fire several powerful rounds that pass through the entire width of the car Tuggle is hiding behind. Tuggle is hit in the chest by one of the shots and dies immediately. Sykes, enraged at his longtime partner's death, takes off after Tuggle's killers.
Rushing into a dark tunnel near the store, the Newcomer Sykes chases pulls out a small vial of blue fluid and deposits a small amount on his tongue. The substance is clearly a drug and the newcomer, invigorated by it's effects, furiously charges Sykes. Sykes fires several shots into the alien's chest, who seems unaffected at first but eventually drops. When Sykes is found by the backup that arrives, one of the officers tries to help him to his feet. When Sykes sees that the officer is a Newcomer, he violently pushes him away and hits him.
The next day at his headquarters, Sykes joins his company for the morning debriefing. Everyone is saddened by Tuggles' death and their captain announces that they'll be taking in a new officer, someone who happens to be a Newcomer, the 1st one to be promoted to detective. Sykes volunteers to take the Newcomer, Detective Francisco, as his new partner, despite his obvious prejudice about their species. Francisco, having taken a new name because his own alien name is unpronounceable, tells Sykes his given 1st name is Sam. Sykes refuses to refer to his partner as "Sam Francisco" so he dubs him "George."
The two go to the coroner's lab where they receive a report about the Newcomer store owner and the alien Sykes shot. While Sykes talks to the coroner, George talks to his Newcomer assistant in their native language. Evidence of a specific condition was found in the murderer but George doesn't share the information with Sykes. George also has an obviously scared look on his face at the news.
Sykes and George continue their investigation and find that another Newcomer, Joshua Strader, a nightclub owner, is their next lead. On a stretch of ocean beach, Strader is being beaten by the henchmen of a Newcomer businessman, William Harcourt, while his assistant, Rudyard Kipling (himself one of the Newcomers involved in the convenience store holdup), looks on. When Strader won't accept a lucrative offer from Harcourt, Harcourt orders his men to take Strader out into the salt water, which has the same effect on the alien species that acid would on humans.
Further investigation by the pair reveals that Strader was quarantined with Harcourt and two other Newcomers who were chemists. Sykes and George talk to the manager of a factory where Newcomers work in a room filled with methane gas without harm. After Sykes and George leave, the manager looks over a room behind protective glass where Newcomers are working with complex machinery to produce a blue fluid like the one the store robber took a dose of before Sykes killed him.