All over the world gold mysteriously vanishes without a trace. MYDO (the Mysterious Yonder Defense Organization) is called in to investigate. The MYDO team, with their secret base disguised as an ordinary gasoline station, and their super aircraft, the Skyfish, set out to discover who is stealing the Earth’s gold. The Alien Benzen is after more than mere monetary gain. Under his control the monster Cottenpoppe sucks up the gold and converts it to energy which is then transferred to Alien Benzen making him even more powerful. To Alien Benzen, pollution is beauty and destruction an art form. Once filled with gold energy, Alien Benzen plans to defile the entire world. The only thing that stands in his way is the MYDO team. Alien Benzen learns that the true identity of ULTRAMAN ZEARTH, the MYDO team’s gigantic protector from outer space, is MYDO trainee Katsuto Asahi. But Katsuto and ULTRAMAN ZEARTH has one weakness; an overpowering fear of dirt and grime. Alien Benzen kidnaps Toru, MYDO member and the love of Katsuto’s life, along with three children and imprisons them on an island in the middle of a filthy lake. On the other side stands the monster Cottenpoppe, threateningly. Using his super-powered electric toothbrush, Katsuto transforms into ULTRAMAN ZEARTH! But ULTRAMAN ZEARTH’s mighty Speshushula Beam is useless against Cottenpoppe. If he fires it, the gold energy stored in the monster will be released all at once, utterly destroying the Earth! To save Toru, the children and the entire world, ULTRAMAN ZEARTH must overcome his greatest fear. But even with the help of the MYDO team can ULTRAMAN ZEARTH withstand the combined power of Alien Benzen and the monster Cottenpoppe?