A mad scientist working in the South American jungle miniaturizes his colleagues when he feels his megalomania is threatened.

Four explorers are summoned to Peru by the brilliant physicist Dr Thorkel. They discover a rich source of radium and a half-mad Thorkel who shrinks them down to one-fifth their normal size when they threaten to stop his unorthodox experimentation.—Steve Hill <[email protected]>

After a former student discovers a rich deposit of radium in a South American rain forest, the brilliant but arrogant Dr. Alexander Thorkel sets up a laboratory there and begins experimenting on miniaturization of animals. When the pupil questions the scientists ethics, he callously murders him. Faced with failing eyesight, the mad doctor enlists three other scientists to help identify the roadblock that has delayed completion of his project. After a long and arduous journey by pack mule through the Andes, they arrive at the laboratory and quickly identify Thorkel's problem. Steve Baker, a miner and fourth member of their party, realizes the value of the radium and is reluctant to leave as are the scientists, who feel slighted by Thorkel's dismissive attitude and their concern about his now growing megalomania and paranoia. Feeling threatened by their curiosity concerning the true nature of his work, he miniaturizes them along with a native servant as they become his de facto guinea pigs. Although their situation appears grave, their one hope lies in Thorkel's Achilles heel, his failing eyesight.—[email protected]

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