The mystery has to do with the murderous rites of the 'Brotherhood of the Dew,' a superstitious sect of the Zulus on the borders of Natal, who had a horrible way of sacrificing human beings in order to bring rain at times of drought. This is only discovered after the mysterious disappearance of two white settlers, one a man not traced till long after, and the second a woman, rescued in the nick of time. While a love interest runs through the story, the more exciting passages deal with the adventures of the hero of the story and of a blundering ex-soldier who accompanies the former on a trading expedition over the border into Zululand. Many narrow escapes and thrilling adventures, usually caused by the ill-concealed contempt of the ex-soldier for the natives, keep the interest well sustained. The author writes as one who knows his subject and locality; a good book for boys of every size.