Dr. Herbert West and his colleague, Dr. Dan Cain, continue their grisly experiments in reanimating the dead, developing a new serum that not only brings corpses back to life but also allows them to create hybrid creatures from different body parts. Working in a makeshift lab located in the basement of a hospital, West becomes increasingly obsessed with creating a perfect human by combining various body parts from multiple sources, including the heart of Cain's deceased fiancée. As West and Cain gather the necessary components, they face mounting suspicion and scrutiny from law enforcement, particularly the determined Lieutenant Leslie Chapham, who is thoroughly investigating the strange occurrences and missing body parts linked to their activities.

Meanwhile, a series of strange incidents and reanimated beings wreak havoc, raising the stakes considerably. The doctors’ experiments spiral further out of control as the pieced-together creatures gain consciousness and exhibit unpredictable behavior. Faced with moral and ethical dilemmas, as well as the looming threat of discovery by authorities, Cain begins to question the boundary between life and death and the consequences of their relentless pursuit of scientific achievement. An escalating series of clashes with the authorities and reanimated entities drives both doctors toward a final showdown where they must confront the horrifying results of their unchecked ambition.