It’s Alive III: Island of the Alive

During a rainy night, a woman goes into labor inside a moving cab. The driver searches for a police officer and a public phone to call an ambulance. While he is away, the baby is born and reveals itself as a mutant, and the officer shoots at it; the infant retaliates by killing the officer and the mother.

The mutant baby's corpse is discovered inside a Catholic church the following day. It drags itself as it dies, highlighting the creature's eerie persistence and otherworldly nature.

In court, Stephen Jarvis pleads for his mutant son's life, arguing the mutation is a reaction to hostility and chaos around him. The baby breaks out of its cage, but Jarvis calms it, and the judge decides to spare the child and four others by quarantining them on a remote island.

After the trial, Jarvis becomes a social pariah, unable to work and shunned by society because of the mutation's stigma. Ellen, the baby's mother, wants to live her own life, as if the birth never happened, deepening their estrangement.

Cabot and his associates travel to the remote island where the quarantined babies are kept, intending to kill them to manufacture the drug under a new label. The babies fight back, killing and consuming the entire party.

Five years after the earlier events, Lt. Perkins recruits Jarvis to join an expedition to the island with Dr. Swenson to study the mutant babies. The voyage proves disastrous: only Jarvis and Perkins survive; Perkins deserts, and Jarvis remains a captive on the boat as the mutants head toward Cape Vale, Florida.

During the voyage, the mutants have grown to adulthood and one has given birth to a baby, with the father implied to be Jarvis's son. The children appear to communicate telepathically and move with a shared will. Jarvis realizes he has survived thanks to the ship's crew's bodies and because his son is protecting him.

The voyage leads to contact with another vessel. In a bid for survival, Jarvis's son throws his father overboard to save himself, hoping the other ship will rescue him.

Jarvis awakens to find himself captive in Cuba. He convinces his captors of his identity and argues that the mutant children pose a danger, persuading them to take him back home.

The mutant children arrive in the United States and kill several people they consider threats to themselves or Ellen. They also defend a woman who is being attacked by killing a gang of punks.

The children locate Ellen and try to persuade her to take the child. Ellen is initially reluctant, but Jarvis convinces her that the mutants act out of love and that the child needs a caregiver.

The mutants die of measles, leaving Ellen to care for the infant. The final adult mutant distracts the police, allowing Ellen and Jarvis to escape with the child. They drive away together, searching for a safe place to raise it.