Amazing Man Comics #19

Rocke Wayburn, a hard-fighting sea adventurer, discovers that foreign spies have kidnapped Mary Flynn, the daughter of an old friend, to extract classified defense information she possesses. Racing to Tartar Island where the spies are hiding, Rocke battles the agents and infiltrates their ship to rescue Mary before turning over crucial evidence to the authorities.

When five ships mysteriously sink in New York Harbor, the Shark—an undersea creature with webbed hands and feet—races to uncover who's behind the underwater sabotage, while his father, Neptune, poses as a land detective to crack the case first. As the investigation leads them through a web of spies, a brewery owner named Samson, and an international operator named Frank Colliers, both father and son find themselves closing in on the truth from different angles. The question is whether they'll stop Colliers' next devastating attack before more innocent lives are lost.