After killing his assistant Dr. Mendoza, the insane Dr. Thorkel summons the biologists Dr. Bulfinch and Dr. Mary Robinson to meet him in a remote area in the jungle of Peru. They travel with the mineralogist Bill Stockton in mules owned by Steve Baker that insists to go with them. After the long journey, Dr. Thorkel asks them to help him to identify a sample in a microscope and after receiving the answer, he thanks the support of his colleagues and say farewell to them. They decide to stay and find that there is a uranium mine in the spot. Further, they break in Thorkel's laboratory to snoop into his research. Thorkel lures the group and locks them and his servant Pedro in a room with an apparatus developed by him. He activates the device and shrinks the group that flees from him. Now Dr. Thorkel hunts them down.—Claudio Carvalho, Rio de Janeiro, Brazil