Not a Serial!
Inventor Harry Harper travels to the South Seas, where there is buried treasure belonging to a girl, Beverly West. Naturally, others are after the loot, and Beverly's father is being held captive by cannibals until she returns to them with a pearl that belongs to one of their idols. The climax consists of Harper saving Beverly from a safe which has been lowered into the sea.
south seas
cannibal
buried treasure