In Los Angeles, Frank Davis (John Ryan) and his wife Lenore (Sharon Farrell) are expecting their second child. Frank is a successful public relations consultant and his wife is a stay-at-home mom for their first child, Chris (Daniel Holzman). The couple avoided having a child for several years while Lenore took contraceptive pills. When their child is ready to be born, they leave Chris with a family friend, Charley (William Wellman, Jr.), and go to the hospital. Their second child, a baby boy, is born monstrously deformed, with fangs and claws. Immediately after birth, one of the doctors attempts to suffocate the child. The child kills the doctors and nurses and flees through a skylight. Lenore is left alive, screaming for her child as a horrified Frank discovers the carnage.
Frank and Lenore are allowed to leave the hospital while the police investigate the killings. Unknown to anyone, the child travels to the Davis home, and kills anyone he encounters. As the killings continue, the press and the police hound Frank and Lenore. When talking with medical researchers investigating the case, Frank is reminded of watching Frankenstein and Karloff's portrayal of the monster. He sees the child as symbolic of the monster and comes to see himself as Dr. Frankenstein, the true monster who created and abandoned the creature. Frank denies the child is his son, and joins the hunt for the murderous infant.
The doctor who prescribed the drugs to Lenore is contacted by a pharmaceutical company executive. The executive acknowledges that the child's mutation may have been caused by the drugs. He tells the doctor that the child must be destroyed to prevent discovery of the company's liability.
The Davis infant reaches the Davis home. Lenore embraces the child and hides him in the basement. Chris becomes homesick and runs away from Charley's house. Charley follows him. Frank discovers that Lenore is hiding the infant. Lenore desperately defends her child and promises he would not hurt the family. Frank then takes a gun into the basement to kill the infant, but he finds Chris talking to him and promising to protect him. Frank shoots at the child and hits him. The infant then flees the basement, and attacks and bites Charley on the neck, killing him. Frank shoots again. Lenore hysterically tries to stop Frank, and Frank tries unsuccessfully to reason with her.
The police track the infant into the sewers, where Frank hunts him with a rifle. When he finds him, he realizes that the child is frightened and will not hurt him. He apologizes to the child and picks him up. Wrapping the baby in his coat, Frank tries to elude the police, but a mob of armed cops confronts him as he exits. He pleads for them to study the child but not hurt him. The fertility doctor screams at the police to kill him. The child suddenly leaps from Frank's arms and attacks the doctor as the cops open fire, killing both the infant and the doctor. As the Davises are being taken home by the police, the detective in charge receives news that another deformed baby has been born in Seattle as the film ends.John P. Ryan as Frank Davis
Andrew Duggan as the Professor
Sharon Farrell as Lenore Davis
Guy Stockwell as Bob Clayton
James Dixon as Lieutenant Perkins
Michael Ansara as the Captain
William Wellman Jr. as Charley
Robert Emhardt the Executive
Shamus Locke as the Doctor
Daniel Holzman as Chris Davis
The film had a complicated release through Warner Bros. beginning in 1974.
Upon completing the film, Cohen found the executives who had backed the production had been replaced and the new executives showed little interest in the project. The studio gave the film a one theater run in May 1974 in Chicago. It was given a limited release beginning October 18, 1974. The film drew respectable business, but the company still did not fully support the project. Three years after its original release, Warner Bros. saw another change in executives and Cohen asked the new group to review the film.
It was reissued in March 1977 with a new advertisement campaign. The new 1977 TV advertisement showed a baby carriage with the music Rock-a-bye Baby playing, then a claw came out and a voice-over said, "There is only one thing wrong with the Davis baby. It's alive". The new ad drew people into theaters, ultimately earning Warner Bros. $7.1 million in U.S. domestic rentals.
It's Alive received polarized reviews from critics. It has an approval rating of 69% on film review aggregate Rotten Tomatoes and an average rating of 5.9/10 based on 16 reviews.
The novelizations of the first film and its sequels expound on the dangers of various prescription drugs administered to expectant mothers during the 1950s and early 1960s (i.e. Thalidomide), the use of fertility drugs, and the indirect use of pesticides on people. In the story, the mother of the first mutant child had a history of taking combined oral contraceptive pills prior to planning her second pregnancy, whereupon she instead began taking an inadequately tested fertility drug to facilitate the conception of her second child.
The film was followed by two sequels, It Lives Again (1978) and It's Alive III: Island of the Alive (1987) and a remake, It's Alive (2009).