At a medical institution in Zurich, Switzerland, a dean is summoned to look into a commotion in one of the laboratories. Upon entering, accompanied by a policeman and a nurse, they encounter Professor Gruber, who is in a state of fear and agony, and Herbert West, a medical student. Gruber's skin has turned an unnatural purple, and his eyes bulge until they pop, spilling blood everywhere. Tragically, he collapses and dies. When questioned by the dean about Gruber's death, West responds with an eerie confidence, saying, > "No, I gave him life!"
West later relocates to Miskatonic University in New England to pursue his studies further. He rents a room from fellow medical student Dan Cain (Bruce Abbott) and transforms the basement of the house into a private laboratory. Tensions quickly arise between West and faculty member Dr. Carl Hill (David Gale), who West accuses of stealing the theory of brain death from his deceased mentor, Dr. Gruber. Hill retaliates by assuring West he will never pass his class.
Meanwhile, Dan is involved in a secret romance with Barbara (Barbara Crampton), the daughter of the medical school's dean, Dr. Halsey. Aware that their relationship could lead to Dan's expulsion if discovered by her father, both Dan and Barbara tread carefully. However, things take a sinister turn when Dan learns that West has successfully re-animated his deceased cat, Rufus, using a glowing “reagent.” West convinces Dan to join him in his groundbreaking research that challenges the enigma of death. This discovery, however, does not sit well with Dan's fiancée, Megan, who is horrified upon learning about Rufus's grotesque revival.
The situation escalates as Hill successfully turns Dr. Halsey against both West and Dan, leading to their exclusion from the medical school. Determined to continue their experiments, West and Dan sneak into the morgue to test their reagent on a human corpse. What follows is a terrifying sequence where the corpse awakens and goes on a violent rampage, forcing Halsey to confront the scene meant to expel them for trespassing. Despite their efforts, Halsey is brutally killed by the re-animated body. Demonstrating an unyielding commitment to his research, West injects Halsey with the reagent, reviving him but at a horrific cost; Halsey comes back in a mindless, zombie-like state.
As the chaos unfolds, Hill learns of West's research and seeks control over Halsey, confining him to a padded room next to his office. Meanwhile, Dan and Megan infiltrate Hill's domain, uncovering evidence of Hill's obsession with Megan and his grim act of lobotomizing her father. Enraged and determined, Hill confronts West in the lab, attempting to blackmail him into collaborating on the research that he seeks to claim as his own. In a moment of fury, West strikes and decapitates Hill, leading to a bizarre resurrection where both Hill's head and body come back to life.
While West conducts a peculiar interview with Hill's severed head, the reanimated body takes control, capturing West's reagent and returning to Hill's lair. Using Halsey as a puppet, Hill orchestrates a kidnapping aimed at Megan. A climactic showdown ensues in the morgue, where Hill's body, wielding its head, confronts Dan and Megan. In a desperate attempt, Megan reaches out to her father, who momentarily breaks free from his undead constraints, allowing Dan and her to escape. In the turmoil, however, Halsey meets a tragic end at the hands of his own creations after destroying Hill's head. West injects Hill's reanimated body with what he believes to be a lethal dose of the reagent, resulting in a horrific mutation that attacks him.
As Dan clutches the satchel containing West's reagent, chaos reigns around him. He and Megan flee, but a reanimated corpse intervenes, resulting in Megan's devastating death. Desperate to save her, Dan rushes her to the emergency room, but his attempts to revive her fail. In a moment of desperation, he injects her with the glowing reagent, leading to a chilling fade-out as Megan screams, hinting at the disastrous consequences of their experiments.
