Madame Lefoux has a contrivance chamber below the hat shop: Chapeau de Poupe. She uses it as a workspace for her inventing and creations. Her aunt, Formerly Lefoux, also resides within the contrivance chamber. Later, when Biffy takes over the running of the shop, the contrivance chamber gets converted into holding cells for the London Pack during the full moon.
- "Beautiful.' Vieve's eyes gleamed. 'Someday I want a whole massive laboratory exactly like this all to myself.' 'Oh?' 'I shall name it my contrivance chamber.' She had clearly given this a great deal of thought." (Etiquette & Espionage, Lesson Eleven)
- "Now that she could see them closer up, the gadgets lying about Madame Lefoux's contrivance chamber were amazing. There seemed to be an entire assembly line of glasscials in midconstruction and a massive apparatus that looked to be composed of the innards of several steam engines welded to a galvanometer, a carriage wheel, and a wicker chicken." (Changeless, Chapter Four)
- "Professor Lyall finally realized what it was about the contrivance chamber that was so different from his last visit: it was quiet. Usually the laboratory was dominated by the hum of mechanicals in motion, steam puffing out of various orifices in little gasps and whistles, gears clanking, metal chains clinking, and valves squealing. Today everything was silent. Also, for all its messiness, the place had an air of being put away." (Blameless, Chapter Three)
- "While we are on the subject, Madame Lefoux, when you have cleared out your contrivance chamber, I thought that might be a good space for us to build the pack a London dungeon." (Heartless, Chapter Seventeen)
- "Since Madame Lefoux had removed all her machines, instruments, and gadgets, the contrivance chamber was a good deal more cavernous." (Timeless, Chapter Three)