Theater of Spies by S. M. Stirling

Luz and Ciara are the perfect partners in and out of the bedroom and well suited for dangerous work they do for the secret Black Chamber. President Teddy Roosevelt is well aware that the assassination of Archduke Ferdinand and the German takeover has serious implications for the U.S. and his money is on two of his best spies, Luz and Ciara. As they travel all over the world engaged in some really violent encounters trying to be one step ahead of the Germans who will do anything to stop them from completing their mission.
Fun but moves at a breakneck pace that involved keeping up with a torrent of different languages and alternative world history, this is one series that is perfect for readers looking for a lot of action, fun but tough women heroines and spies who seem to really enjoy the danger.