Don Winslow was a veteran of the first World War and a member of the agency of naval intelligence. The agency had Don handle threats such as villains with names such as Dr. Centaur, the Dwarf, the Crocodile, Dr. Q, and the Scorpion. He also battled Singapore Sal a villainous pirate who also fought fellow sailor Lance O'Casey. He was assisted by Lieutenant Red Pennington and dated nurse Mercedes Colby. Mercedes was the daughter of Don's commanding officer Admiral Colby.