After the body of John Grubowsky, a bacteriologist at the top-secret Brandt Research in Peckham, California, is discovered in a local motel, the coroner determines that the scientist died from a massive coronary brought on by strenuous sexual activity. Police captain Jim Peters is puzzled by the finding, as Grubowsky had no history of heart trouble, and when another man is found dead under similar circumstances, he notifies the State Department. Neil Agar, a State Department security agent, soon arrives from Washington and meets Julie Zorn, Grubowsky’s assistant, at the Brandt facility. Although she is the last person to have been seen with Grubowsky, Julie convinces Neil that she was not with her boss at the motel. Attracted to Julie, Neil invites her to lunch at the facility’s dining hall. There, Julie points out reproductive biologist Dr. Henry Murger, who, unlike the other male scientists at Brandt, has never been seen in the company of women. In a nearby country field, meanwhile, a naked woman on a motorcycle rendezvous with a waiting man, and the two make love in the grass. At the end of the act, the man dies, and the woman calmly walks away. Soon after, another man winds up dead in a motel room following sex with a beautiful stranger. Grubowsky’s widow Gretchen then receives a phone call from a woman who claims to have been with Grubowsky in the motel and insists they meet. Later, over drinks at the Brandt dining hall, Neil questions Herb Kline, Stan Williams and Aldo Ferrara, Grubowsky’s fellow scientists, and notes the arrival of Dr. Susan Harris, the head of the facility’s entomological department. Despite her beauty, Neil is assured that Susan, who wears large, dark sunglasses, is frigid and disinterested in men. When two more local men are found dead from sex-induced heart attacks, the sheriff calls a town meeting to announce a curfew. As a precaution Henry urges the townspeople to be sexually abstinent, angering Barney Braddock. That night, after complaining about Henry’s restrictions at a bar, a drunken Braddock is approached on the street by a strangely seductive Gretchen, who lures him into her car. Henry, who earlier had announced that he was close to figuring out the cause of the deaths, then is run over and killed by an unidentified woman driving Henry’s car. Neil, who is nearby with Julie, rushes to the accident site, then leaves Julie to call the State Department from a phone booth. While he is arranging for a military quarantine of Peckham, Julie is attacked by three men, but Neil returns in time to save her from being raped. Later, Neil goes to Henry’s house to look for information about his recent findings and there discovers a secret “sex” room. When a burly man named Joe sneaks in, Neil beats him up and forces him to admit he was Henry’s homosexual lover. The next day, Herb agrees to have dinner with the suddenly flirtatious Susan and, as Neil listens, lies to his wife Nora about his evening plans. At her house, Susan continues her seduction of Herb, feeding him a sweet concoction before disrobing. As Susan begins to make love to Herb, her eyes grow extremely large and black, like an insect’s. Sweating and panting, Herb dies in Susan’s arms, and afterward, Susan phones Nora and tells her they must meet. At Julie’s, meanwhile, she and Neil watch a movie about insects, having concluded that the town’s deaths are somehow connected to Susan’s work. The next day, Neil questions Susan at her laboratory, and she tells him that queen bees stop mating once they are impregnated by drones, whom they kill after sex. After abruptly dismissing Neil, Susan rushes to a restricted radiation area, where she and four other women, including Gretchen, are holding a naked Nora captive. Susan injects Nora with a powerful sedative, then the other women slather Nora with a sticky substance, enclose her in a transparent chamber and release thousands of bees that cover her body. Afterward, Nora emerges from the chamber, beautiful and seductive but sporting large, black eyes. Later, Neil and Julie confer with Stan and Aldo, and Aldo agrees with Neil that forced genetic mutation, resulting in a bee-human hybrid, is possible through radiation. To prove their theory, Julie and Neil attend Grubowsky’s funeral armed with a photosensitive, gamma-counting camera and take pictures of Susan, Gretchen and several other women in large sunglasses. That night, Stan’s normally staid wife Harriet tries to seduce him, but he realizes that she has been transformed and strangles her. When Neil then goes to retrieve Aldo’s tape-recorded research notes, he finds the scientist dead and hears Susan’s threatening voice on Aldo’s tape. Aware that Julie is meeting with Susan, Neil rushes to the lab, arriving just as Susan and the other women are placing Julie in the chamber. Neil shoots the lab’s computerized control panel, causing the machine to explode and burn, and rescues the dazed Julie. Trapped inside the fiery lab, Susan and the others, however, die. Later, Julie explains to Peters that because the radiation rendered the “bee” women infertile, they were compelled to continue mating and killing. That night at Julie’s, Neil begins to make love to Julie, as a faint buzzing sound fills the air.