For his second commercial feature, following a pair of experimental films and 1977's Shivers, Canadian horror auteur David Cronenberg continued to mine the themes of disease and mutation that were already becoming his perennial concerns.

Marilyn Chambers stars as Rose, an attractive young woman who becomes horribly injured in a motorcycle accident. Spirited away to the clinic of Drs. Dan and Roxanne Keloid (Howard Ryshpan and Patricia Gage), a pair of experimental plastic surgeons, Rose becomes an unwitting guinea pig in an operation that grafts genetically modified tissue into her body. Waking from her coma to find she is unable to ingest normal food, Rose unwittingly feeds on human blood by means of a phallic organ that emerges from a vulval orifice in her armpit.

Within hours of providing Rose with sustenance, her victims fall prey to an incurable, highly contagious disease that turns them into raving lunatics who foam at the mouth and attack others indiscriminately. Soon, Montreal is under martial law, but nobody can find the Typhoid Mary whose vampiric urges are driving the epidemic -- not even Hart (Frank Moore), Rose's befuddled boyfriend.