Set on Sullivan's Island in South Carolina, the story follows William Legrand, his servant Jupiter, and a young medical student. Legrand was living on Sullivan's Island in a beach hut. It was a lonely spot, and few people would guess that the island was inhabited. On one of his visits, Legrand tells the young man about a gold scarab-type bug which he has captured, which Jupiter is convinced is made of solid gold. Secret codes, cryptography, adventure, and buried treasure are just a hint at what follows!