A school boy, Mamoru, witnesses and retrieves a small, lightweight meteorite, which coincides with another falling into the Libyan Desert. When they begin to emit signals into space, Professor Ichinotani decides to investigate the object that fell in Japan, which the locals have nicknamed "Garadama". While searching the area, yet another giant meteorite crashes into the dam reservoir, sending boats scattering while the tremendous heat evaporates the entire lake. Not long afterwards, a strange monster breaks out of the meteorite, as Jun and Ippei set out to rescue two girls trapped in a boat stranded high on a precipice.
熊谷ダム付近で発見された異常に軽い隕石。落下地点に調査へと向かった一の谷博士、万城目たちの前でダムに隕石が落下。湖水が一瞬にして蒸発し隕石怪獣ガラモンが現れた！
