The author of The Sun Shall Greet Them (the finest story of Dunkirk, but one that came too late for deserved popularity), has written a first rate adventure story molded around the theory that the Nazis might drill a tunnel for invasion under the Channel. An ardent youngish engineer is investigating his theory, in spite of disbelief of his superiors. But he convinces the hero of the story, a Naval intelligence officer, and together they plunge into complexities of machinations round and about Dover. A local poacher supplies some of the needed clues; an elderly intellectual and his charming daughter do their share. The result is not only good entertainment but a good picture of civilian defense, of village psychology, and of England under fire.