A superior adventure entertainment spends most of its time underground- in the caves of the Austrian village of Frohnberg, and for those not under the spell of speleology, there is an attractive romance. The Herrins, Cynthia and Henry, an English couple, return each summer to Frohnberg to cave- where for the first time they meet the young Graf Frohnberg, a former Russian war prisoner whose experiences have left him only with a taste for death. Cynthia, attracted to another man for the first time since her marriage to Henry, is caught by the realization that she cannot salvage him and guilt also brings its bitterness. Cynthia and the Graf, along with a honeymoon couple- Heather and Peter, join Henry on one of his explorations and they are all trapped there when a tunnel wall crumbles. With few supplies, they try to make their way underground through the warren of tunnels and caves, rivers and lakes. Peter drowns, and Hesther deliberately follows him; and finally, as they make their way nearer the surface, Cynthia is forced to choose between her husband or her lover- as one only can survive with her.... A genuine cliffhanger- and the subterranean world lends a very special background to danger with much the same appeal of the early Hammond Innes books.