Black Chamber — S.M. Stirling

The first novel in a brand-new alternate history series where Teddy Roosevelt is president for a second time right before WWI breaks out, and on his side is the Black Chamber, a secret spy network watching America's back.

1916. The Great War rages overseas, and the whole of Europe, Africa, and western Asia is falling to the Central Powers. To win a war that must be won, Teddy Roosevelt, once again the American president, turns to his top secret Black Chamber organization--and its cunning and deadly spy, Luz O'Malley Aróstegui.

On a transatlantic airship voyage, Luz poses as an anti-American Mexican revolutionary to get close--very close--to a German agent code-named Imperial Sword. She'll need every skill at her disposal to get him to trust her and lead her deep into enemy territory. In the mountains of Saxony, concealed from allied eyes, the German Reich's plans for keeping the U.S. from entering the conflict are revealed: the deployment of a new diabolical weapon upon the shores of America...