In the opening scene, a group of pirates relaxes after a successful raid when one of them discovers a strange metal mask and ventures into a dark cave, only to be sucked into a hole.

The narrative shifts to Warren Price, the son of a millionaire, who is on an expedition to explore a former Japanese military bunker on the Indonesian island of Una-Una. He is accompanied by his girlfriend, Su-Ling, and a Japanese scientist named Rie, along with a team of mercenaries led by Captain Tino Prawa and including Stanley, a former military engineer.

As they journey, the group hears screams from a cave, which turns out to be a prank by Sergeant Papa. Warren reprimands Tino for his men’s behavior, but Tino assures him it won't happen again. As they investigate the cave, Rie indicates they are nearing their objective. Outside, Stanley questions Tino about the mission's purpose, but Tino admits he prefers to stay uninformed.

Continuing their trek, they discover an entrance to a dead mine. Rie explains its history, suggesting it was originally Dutch before being taken over by the Japanese after World War II. Warren theorizes that the mine was converted into a military bunker, aligning with their mission's goals.