Three boys just out of school run across an unusual rock-like shell that falls off a truck at a construction site. Naturally they believe it to be some sort of fossilized monster egg (from 'the Jurassic Era', as one kid puts it). Shortly thereafter a burrowing creature emerges from the side of a mountain near the building site. MAT is on the scene but fails to obliterate the beast with bombs after Goh sees a little girl on the ground nearby. This refusal to follow orders gets Goh placed under house arrest for three days. Meanwhile, a second creature appears, and a battle ensues between both monsters and Ultraman.
工事現場で岩石状の物体が発見された。処理をめぐって郷と岸田の意見が対立するなか、砕石場に地底怪獣グドンが出現する。一方、岩石状の物体からは古代怪獣ツインテールが現れ、新宿副都心はパニックとなった。郷はウルトラマンに変身してツインテールと戦うが、そこにグドンも現れ……
