Selene and her best friend, Beatrice, are Boston librarians during WWII.  For different reasons, they agree to go to Lisbon, Portugal to work as Allied spies.  Lisbon was known at the time as a safe city that was neutral in the war.  As a result, operatives from both the Axis and Allied powers worked in the city at the behest of their governments. Ostensibly, the two librarians are there to rescue books from the volatile area and send them out of the country to safety. The two women end up with different assignments and each of them ends up paired with one of Lisbon's most notorious men. 

Luca Caldeira is a Portuguese baron whose brother is responsible for supplying a critical product, Wolfram, to both the Axis and Allies; in equal amounts.  Balance of power and all that, you know. Selene thinks she is using Luca to further her undercover work but finds herself falling in love with him and she isn't terribly sure if the Caldeiras are being honest about the supply of Wolfram from their mines.

Bea finds herself immersed in the OSS' administration which might have proved boring in the long run had she not been assigned to personally help the OSS' most notorious spy in Lisbon, Gable.  Determined to show both Gable and her supervisors that she is capable, she resists the siren call of Gable's enigmatic nature - as long as she can.

The women are separated by the need for secrecy so neither suspects the other is working towards the same goals: determine if Germany is getting a larger share of Wolfram than they are entitled to, and to discover who a murderer is who is targeting high-profile people that the Allies are trying to rescue.

This is obviously a well-researched story and the plot was interesting.  The two women were well-described; the men a little less so.  But that's to be expected as the story is about the two women and what these events do to their friendship.  It had good pacing, decent world-building (not terribly necessary but not everyone understands Portugal's role in WWII), and good characterizations. The love stories did tend to take over the story-telling; this reader would have enjoyed more detail about the desperate nature of people who came to Lisbon to find a way off the continent.  So, be aware that this is more a love story than a nail-biting WWII espionage thriller.  But I did enjoy the story; I can recommend this.  ~~ Catherine Book