Lady Friday

Lady Friday was Mistress of the Middle House, keeper of the Fifth Part of the Will and the Fifth Key. She is afflicted with Lust, which manifests in her insatiable desire to "experience" mortals: a vampiric practice of draining mortals of their emotional experiences, similar to Dementors in Harry Potter and the villain Spyder from Marvel Comics' New Mutants. She is briefly mentioned in Grim Tuesday when Tuesday refers to her as "that fool Friday". She masquerades as a doctor on Earth, calling herself "Doctor Friday", and uses this guise to steal mortals, whose memories she then drains to feed her addiction.

Lady Friday sent heralds to the Piper, Saturday, and Arthur, telling them that she had abdicated her rule of the Middle House and control of the Fifth Key; the first of the three to find and claim it may use it and control the Middle House. The Fifth Part of the Will remains incarcerated so it will not take the Fifth Key, but is no longer under the supervision of Friday. Though Lady Friday claimed she had extended this offer because she wished to abdicate from her role as Trustee and quietly pursue her own personal interests, her offer was actually a trap to dispose of the Piper, Saturday, and Arthur.

In truth, Friday has taken the Fifth Key (a mirror) with her to her mountain retreat in Avraxyn, a Secondary Realm in the Lesser Magellanic Cloud (ironically the planet where the mold symbiotic with the Spirit-Eater resides), in order to continue "experiencing". Arthur defeated her, claimed the Fifth Key, and placed her under arrest. Lord Sunday correctly accuses Dame Primus of murdering Lady Friday, although it is unknown how she died. As she was taken in the Advance Guard that fled from the dissolving Great Maze, she was probably abandoned or thrown into the many Nothing Leaks. It is also possible that she had never been actually evacuated but instead killed secretly by the Will in an unspecified way, since it is the Will who says she has been evacuated, but no one ever supports or confirms this.