The film opens with an American archaeological expedition to the kingdom of Siam (modern Thailand) in Southeast Asia. While examining a number of tombs, the archaeologists locate a sealed crypt. Within the crypt, they discover an idol in the form of a scorpion, and eyes made from quartz lenses. When the lenses are properly aligned, a powerful energy beam emerges and instantly causes an explosion.The archaeologists realize that they have found a powerful weapon of unknown origins. The lenses are divided among the members of the group, to ensure that none of them may operate the weapon on his own. Meanwhile, the wizard Shazam chooses one of the youngest members of the expedition, the radio journalist Billy Batson, to grant him the power to shape-shift into the heroic Captain Marvel. Shazam informs the hero that the idol is cursed, and that his mission is to protect those in danger from the curse's effects. When this task is completed, Shazam will depower him.Following the expedition's return to the United States, a mysterious super-villain starts operating. He is codenamed "Scorpion", and he steals the idol after which he is named. Scorpion then starts locating and killing various members of the expedition, in order to recover the various lenses. Captain Marvel repeatedly fails to stop the Scorpion, but soon notices that the Scorpion seems informed of everything discussed in meetings between the surviving members of the expedition. Marvel deduces that one of the expedition's members is a traitor, and is using the Scorpion identity to eliminate his former allies.The surviving expedition members realize that there is one missing lens, which was somehow forgotten within the crypt. They decide to return to Siam to retrieve it. During this second expedition, Scorpion steals the missing lens and finds out the secret identity of Captain Marvel.. He kidnaps Billy Batson, but does not realize how the boy's shape-shifting powers work. Batson transforms to Marvel while in captivity, and then unmasks the Scorpion. The villain is soon after eliminated by a Siamese native who knows how to operate the idol properly.Marvel is convinced that the idol has a corrupting influence, and that more villains could follow in the Scorpion's footpath. So, he throws the idol and all of its lenses inside an active volcano, where they are destroyed by the molten lava. Captain Marvel has completed his mission, and Shazam quickly depowers him. Billy Batson is free to return to civilian life.