On a remote island far off the coast of Japan, a strange energy permeated the humid air. Birds dared not venture too close to the isle, and every craft that became ensnared in its deadly current wound up shipwrecked in its shallow waters. The foggy island appeared desolate, with the exception of a thriving population of grotesque fungus. At first glance, these mushrooms, called the Matango, appeared so innocent; however, they had an awful dark side...

In the early 1960s, a scientific expedition from an unknown nation was secretly deployed to research the adverse effects of radiation on the environment, and the expedition's vessel accidentally stumbled upon the island of the Matango. Unable to escape the current, the crew slowly succumbed to the need for sustenance. In time, each crewmember, one by one, ingested the mysterious and delectable Matango. As a chilling result, each one became a living abomination: a walking, involuntary symbiosis between human and fungus. These mutants sought only to assimilate more of their crew into the collective, and ultimately, every member of the research team disappeared into the steamy mists of the island's jungles...

Over a year passed, and a pleasure craft marooned on the rocky coast of the jagged island, as well. The seven passengers were trapped on the island, but as luck would have it, they located the abandoned research vessel and managed to procure provisions. Strange things began to happen; however, when an amorphous, humanoid beast was sighted lurking around the ship. Unfortunately, time progressed, provisions dwindled, and tragedy struck! Etsuro Yoshida succumbed to the allure of the Matango, and his mental state dwindled. He became virtually inhuman, and began to harass and intimidate his fellow castaways. Upon murdering Senzo Koyama, Etsuro was banished from the ship by Fumio Kasai, along with Mami Sekiguchi, who had assisted the twisted author. The rains came, the mushrooms blossomed, and in time, Fumio had become more desperate. He begged and pleaded with Mami for relief! Having already ingested the Matango, Mami's poisoned mind was now bent on one goal: adding to the collective. She led Fumio to the Matango like a pig to the slaughter...

The skipper, Naoyuki Sakeda, had already died out at sea, after attempting to sail to safety. Thus, only two of the original crew remained: Akiko Soma and Professor Kenji Murai. Alas, the full attack of the mushroom people began! Akiko was dragged to the colony of Matango, and when Kenji saw his lover amalgamated into the collective tribe of sinister fungi, he could only run in terror. He took the ship, which had drifted back along the current after Naoyuki's death, and sailed for the mainland. His desire for nourishment was too great, however, and along the way, he too fell under the spell of the Matango. His inability to fight temptation left his body bubbling with a repugnant, festering fungus. He was rescued, but what hope could he find, even in Tokyo? He reasoned that he would have been better off left in that strange and horrible jungle, with the woman he loved...

Back on the island, the passengers of that ill-fated vessel continued to morph into their new, repulsive forms; each one continued to become another mindless slave of the collective. If there were any ship fateful enough to flounder in the dangerous waters of that reviled isle again; the hideous Matango would most definitely prevail over humanity once more. The insidious mushrooms were always waiting...