It's 1943 and the tides of the Second World War are changing: the Germans are losing and the Allies are on their way. Special Operations Executive, Saffron Courtney - daughter of the celebrated soldier Leon Courtney - is sailing from the west coast of Scotland to New York on the Queen Mary. Her mission is two-fold: to gather support for SOE, but, more treacherously, to uncover a Nazi spy ring and a mole deep within the British Embassy. As Churchill and Roosevelt, two of the most powerful men on earth, are about to begin talks that will determine British and American military strategy for the next two years, it is vital that the enemy don't find out their secrets.

Meanwhile, what Saffron doesn't realise is that while she is on the tail of a dangerous spy, there are equally dangerous agents after her, desperate for justice following the death of Hauptsturmführer Schröder, a powerful Nazi she killed in self-defence. With time running out, and the safety of not only the nation, but Saffron herself, under threat, can she uncover the truth and expose the dangerous plots before it's too late?