Astronaut Steve West becomes the sole survivor of a disastrous space mission to Saturn, exposed to mysterious cosmic rays that cause his body to undergo a grotesque transformation. Returned to Earth, he’s kept in a secret hospital ward where doctors are baffled by his rapidly deteriorating condition. Steve's flesh begins to melt, and he discovers he can only stave off the degeneration by consuming human flesh. Plagued by bouts of disorientation and overwhelming hunger, Steve escapes from the facility, leaving a trail of horror in his wake as his mind and body continue to unravel.

Meanwhile, Dr. Ted Nelson, Steve's friend and one of the lead scientists trying to unravel the mystery of his condition, embarks on a frantic pursuit to find him. As panic spreads, authorities attempt to contain the situation, while Dr. Nelson struggles with ethical dilemmas over his duty to his friend versus the safety of the public. He's torn between his compassion for Steve and the realization that the melting astronaut poses a deadly threat that must be stopped.