Another boys' mystery starring Tommy Rockford and his friend Spud. As in S.O.S. At Midnight (1957, p. 6) and CQ Ghost Ship (1960, p. 151) the ham radio set is the major prop. This time it involves the boys in international intrigue as they set out on a diving expedition to recover the remains of a Spanish galleon. In terms of melodrama and action this follows the pattern set by the first two books.