Setting -- countryside near Doylestown, Penna. And once again Davis goes outside the profession of criminology for his set-up. Last time it was a newspaper; this time it is a doctor and a young mathematician, brought together to create an indecipherable cipher for war use. Danger hovers, striking twice to prevent their success; there are suspects galore, for the work is going on in the midst of a strangely assorted houseparty, snowbound. A story with atmosphere, suspense, originality -- which make one overlook some loose threads when the solution is finally reached. Good yarn, first and last.