Janice Capshaw is pursued and killed by a pack of mysterious, nightmarish beasts while on a nighttime jog along the beach of her northern California home of Moonlight Cove. Sam Booker, an undercover FBI agent, arrives in Moonlight Cove to investigate the recent rash of suspicious deaths, including that of Capshaw. Tessa Jane Lockland, sister of Capshaw, also arrives in Moonlight Cove to investigate her sister's death. Chrissie Foster, an eleven-year-old girl who lives on a farm north of town, accidentally witnesses her parents in a physically altered state - part-human and part-beast - and is forced to flee for her life. She heads towards town to seek help. Sam, Tessa and Chrissie are all separately hunted by the mysterious beasts. Sam and Tessa meet by chance in a laundromat where they have both retreated after being stalked by the beasts. Mistrustful of one another at first, they realize that to survive they must work together. Sam discovers that Thomas Shaddack, a brilliant computer scientist, is converting the citizens of Moonlight Cove into something unexplained. Sam also learns that the local police are aiding Shaddack in the conversions and that their state-of-the-art computer system, given to them by Shaddack’s company, is unnecessarily sophisticated for the needs of a small town police force. Because of a letter sent to the FBI by Moonlight Cove resident, Harry Talbot, offering information about the recent disturbing events, Sam and Tessa decide to go to Harry at his place of residence. Harry is a Vietnam vet, who was badly injured in the war and now uses a wheelchair. He has not yet been ‘converted’. Because he spends most of his time watching the people of Moonlight Cove through his telescope, Harry has learned a great deal about what is going on and also learns that the local police are involved. Chrissie also ends up at Harry Talbot’s, after her attempt to approach the local church ends with her having to evade the beasts again, and she makes the reasoned guess that Harry may be a safe person to approach. Together, the four protagonists piece together more fully the story behind the happenings of Moonlight Cove. Thomas Shaddack has created a means whereby a person can be converted into a super-human - no longer susceptible to illness, injury, fatigue, or emotion. But the conversion has an unforeseen side-effect: stripped of the capacity to feel human emotion, life becomes intolerably meaningless, and most of the newly converted townspeople regress irresistibly into a beast state, concerned only with hunting, killing and consuming their prey. As events unfold, Shaddack descends further into madness. He refuses to acknowledge that his plans have gone terribly wrong and that the conversions should be stopped. Seeing that nothing can stop the town's descent into chaos, the Chief of Police, Loman Watkins, vows to kill Shaddack, which will also kill every converted person in the community: as part of the 'conversions', Shaddack has placed a microchip inside each person that will kill them if Shaddack’s heart ceases to beat. The final showdown takes place at the local high school, after Sam heads there to use a school computer terminal to get a warning to the outside world and request assistance. Shaddack is killed in the confrontation, which kills most of the populace with him. Sam, Tessa and Chrissie survive and the FBI arrive to clean up the mess.