"with an important member of the French underground"

“French underground” is an informal term for La Résistance française (the French Resistance), the collective term for an array of secret armed movements that pursued guerilla activities against the Nazi occupation and the Vichy government that collaborated with the Germans during World War II.

In addition to sabotaging occupation installations and activities, the Resistance collected intelligence information for the Allies, published underground newspapers, and maintained hiding places and escape networks for Allied soldiers and airmen trapped behind enemy lines. The initially clandestine Resistance newspaper “Combat” had such famous contributors as Albert Camus, Jean-Paul Sartre, and André Malraux.

The idea that a member of the French underground would be smuggling frozen eclairs is of course absurd.