François, Lisa et Eusèbe poursuivent leur combat. Le réseau Lynx a dorénavant pour mission de protéger un « pianiste », un espion en charge de l'émetteur-récepteur qui permet à la Résistance locale de communiquer avec Londres.
France has been under occupation by Nazi Germany for over two years now, and the French population is suffering under shortages, forced transfers to factories in Germany, constant propaganda, conflicting political views, and the brutal presence of a new pro-Nazi French militia. Nevertheless, hope remains alive as German troops are experiencing their first major defeats, and the Resistance network keeps growing. Communication with London is steadily improving too as radio operators risk their lives to transmit from inside the Occupied Zone. The children's new mission is to help these operators get their coded messages to the Allies... Easier said than done!