Dark Interlude

For five years he had tortured, mutilated and put to death British secret agents. Now the war was over, only one execution remained - his.
Shaun Aloysius O'Mara, intelligence agent for the British 'second bureau', has been ordered by his superiors to go to Paris to obtain information that will lead to the capture of the lone survivor of the Nazi espionage system.
So when Shaun arrives in Paris he becomes a crude and shiftless drunkard and entangles himself with a clever and ruthless spy, Tanga de Sarieux, who is as brave as the men that surround her...
Dark Interlude was originally published in 1947.