Dr. Nam Gung, escorted to Earth by Thunder, is reborn as a cyborg. Dr. Nam Gung kidnaps Dr. Kim's blueprints and his daughter, helping Space King Ling Gu from the asteroid base conquer Earth. The Earth Defense Legion and Thunder V stand against their ambitions, but the situation becomes increasingly precarious due to the attacks of Thunder, who has turned against them. However, Hyung Rae's transformation into Esperman greatly contributes to regaining Thunder and disconcerting Ling Gu. The powerful robot Black King is also spectacularly defeated before Thunder. Cornered, Ling Gu, who tries to escape using Mina, is shot dead by Dr. Nam Gung, who has regained his memories. The monstrous planet explodes outside the atmosphere. Amidst cheers, the Thunder team returns to Earth.