An adolescent mystery entertainment for girls featuring underwater detection and aerated dialogue. The setting is an island in Polynesia. It has to be. Anywhere else there wouldn't be the taboos that keep the proper island from being investigated right at the start instead of right at the end. There, Nancy's sea captain father, his native crewman and a passenger have been surviving like Robinson Crusoes after the schooner was sabotaged, while at home, a few sea miles away, his daughter and his passenger's sister are wildly surmising. Childlike natives submit happily to the directives of the two teenaged girls, who get to the bottom of The Road Under the Sea, which leads to archaeological discoveries of even greater significance than the artifacts that were central to the author's last -- The Secret of the Maori Cave (1964, p. 897, J-283). A South Sea burble.