City of Spies by Mara Timon

Second Hand 

"Lisbon, 1943. When her cover is blown, SOE agent Elisabeth de Mornay flees Paris. Pursued by the Gestapo, she makes her way to neutral Lisbon, where Europe's elite rub shoulders with diplomats, businessmen, smugglers, and spies. There she receives new orders - and a new identity. Posing as wealthy French widow Solange Verin, Elisabeth must infiltrate a German espionage ring targeting Allied ships, before more British servicemen are killed. The closer Elisabeth comes to discovering the truth, the greater the risk grows. With a German officer watching her every step, it will take all of Elisabeth's resourcefulness and determination to complete her mission. But in a city where no one is who they claim to be, who can she trust?"--Publisher.