While the Great War raged across the trench-lined battlefields of Europe, a hidden conflict took place in the distant hinterlands of the turbulent Mexican Republic. German officials and secret-service operatives plotted to bring war to the United States through an array of schemes and strategies, from training a German-Mexican army for a cross-border invasion, to dispatching saboteurs to disrupt American industry, and planning for submarine bases on the western coast of Mexico.

Bill Mills tells the true story of the most audacious of these operations: the German plot to launch...