While investigating a faint Gaiark signal at a mountain, the Go-ongers encounter a boy named Hiroshi and his younger sister Miyuki who are helping their archaeologist father Rokuro Kuroiwa in his search for a legendary treasure. Though Rokuro attempts to drive the group out after they caught a glimpse of the map, S?suke and Hant decide to help the man in finding his treasure, the Golden Dragon, while the others remained with Hiroshi and Miyuki and learn of Rokuro's dream. But once at the entrance, Drill Banki appears under orders from Yogostein to take the map from Rokuro as the Golden Dragon may be the legendary and extremely powerful Savage Machine Tribesman Horonderthal who came to Earth during the Cretaceous which the minister intends to revive. After over powering Go-on Red and Go-on Green, Drill Banki takes the map from Rokuro and starts drilling his way to the Golden Dragon, closing the entrance. After taking Rokuro back to shack, with the man apologizing to his children for failing them, the Go-ongers promise not to let the Gaiark rob him of his dream. With Rokuro's knowledge of the area, the Go-ongers find an alternate way into the underground tunnels and use the Super Highway Buster/Wing Booster combo to take out Drill Banki. However, the attack reveals the Golden Dragon, with Drill Banki Industrial Revolutionizing as Engine-Oh G9 is formed to stop him from taking the Golden Dragon. But just as it is about to win with the Go-Roader's help, the Golden Dragon whirls to life and emerges from the cave, revealed not to be the Horonderthal but a trio of train Engines as they ram into Engine-Oh G9 before driving off Drill Banki and then flies off with Rokuro and his children watching the Golden Dragon taking its leave. Though the family thanked them for making their dream come true, the Go-ongers decide to find the mysterious Engines.