During World War II in Nazi Germany, Nazi officers confiscate the living heart of the Frankenstein Monster from Dr. Riesendorf and pass it on to the Imperial Japanese Navy, who take it to a research facility in Hiroshima for further experimentation. As the experiments begin, Hiroshima is bombed with a nuclear weapon by the Americans. 15 years later, a feral boy runs rampant in the streets of Hiroshima, catching and devouring small animals. This comes to the attention of American scientist Dr. James Bowen and his assistants, Drs. Sueko Togami and Ken'ichiro Kawaji. A year later, they find the boy hiding in a cave on a beach, cornered by outraged villagers. Bowen and his team take care of the boy and discover that he is building a strong resistance to radiation.