Not much is known about her other than her apparent French nationality, but she appears to enjoy racing in biplanes. In a way, this makes her something of an enigma, even compared to other members of the Fox family. Not even Carmelita Fox knows much about her. However, she believes Joan could be working for the French government.
According to Otto van Cooper, he had just beaten Joan in a race before his plane was shot down by Gustav Gale. Once In the Air Tonight is finished, it is revealed that Joan de Fox was knocked out by some falcons when Otto was captured. This special dialogue can only be accessed in a secret area, where Joan de Fox will be lying down on a couch congratulating the player for defeating Gustav and Amber. Joan will task the gang with finding all of the Secret Masks in the game, including the ones given to the Cooper Gang by Carmelita's other ancestors. Once the side quest is successfully completed, she will reward the player with the final Secret Mask, which in this case is a Secret Penelope Mask, if the player manages to find the rest of them.