This is Nazi-occupied Paris, the girl is a German who lives on the Germano-French border, speaks fluent French and is working in Paris as a translator for the Nazis. And gradually the two come to love each other, which of course poses many difficulties: Maria has to keep this from anyone she knows and works with, as does Marc, especially as he is occasionally working with his father in the Resistance.
Suspicion arises on the part of the Nazis, the lovers have to tighten up on their movements, and all the time discovery seems to be creeping closer to them until for no apparent reason Maria is called back to Germany. Heartbreak on Marc's part of course, but soon he's working full time for the maquis under a different, younger name before the Nazis catch up with him. He lives in the hope that peace will soon come and he will be able to join Maria.
Peace of course comes although Maria was killed a year previously in an air raid and Marc is left to the grief of his first aborted true love. A moving story which called to mind André de Richard's La Douleur .