Madamoiselle de Neuf was the identity of Seven of Nine in the French Resistance holodeck simulation created by the Hirogen. A munitions expert posing as a piano singer, Mlle. de Neuf was a member of the French Resistance movement against Nazi Germany's occupation of France during World War II. She was suspected of being a Nazi spy by one of her colleagues.
Through the use of an implanted neural interface, the crew of the USS Voyager believed that they were the characters in the simulation. Seven of Nine's real identity was restored by the Doctor; however, she continued to play along with the simulation, unbeknownst to the Hirogen. After disabling the crew's neural interfaces, Seven of Nine and Captain Janeway were able to stage a counterstrike with support from the holographic characters. Seven later developed a photonic grenade which disabled holographic activity on part of the ship, a crucial event which allowed Captain Janeway to defeat the leader of the Hirogen and return control of the ship to the Starfleet crew. (VOY: "The Killing Game, Part II")