Puerto Rico has become the back door by which a criminal syndicate smuggles inexpensive contraband diamonds from South America into the United States, dramatically driving down the price of legitimate gems. After they have ruthlessly murdered a special investigator, Moto is assigned to the case. While sailing to the island he impresses Twister McGurk, a slow-witted but amiable wrestler, with his martial arts abilities and gains a loyal friend and bodyguard. When an attempt on his life fails and another government official is murdered, Moto sends authorities a fake telegram identifying himself as a criminal named Shimura and making him and the Twister wanted fugitives. That ploy allows them to infiltrate the gang and expose the criminal mastermind behind it.
Mr. Moto in Danger Island
The U.S. government asks Mr. Moto to go to Puerto Rico to investigate diamond smuggling after an earlier investigator is murdered.
