Dr. Charles Decker, a botanist, returns to London from Africa after surviving a plane crash. He brings back a small chimpanzee named Konga, mysterious seeds from carnivorous plants, and newfound theories about growth. Decker experiments with the seeds, creating a serum that he injects into Konga, causing the animal to grow rapidly. Using his control over the now larger and more ferocious Konga, Decker plans to eliminate those he sees as obstacles to his academic and romantic ambitions, including his colleague and rival, Professor Tagore. Meanwhile, Decker's loyal assistant, Margaret, becomes increasingly uneasy about his ethically dubious experiments and growing madness.

As Konga continues to grow, Decker’s megalomania spirals out of control and his actions draw the attention of both law enforcement and the public. His ruthless use of Konga as an instrument of murder sets off a series of events that threaten to unleash chaos. The botanical discoveries, initially appearing as scientific marvels, quickly turn into the sources of horror and destruction. As tensions escalate, those around Decker must navigate the dangers posed by both the scientist’s unhinged ambitions and the monstrous creature he has created.