A play by an unknown author in which the events of the end of Yhtill are dramatized. At every performance of this play that gets to the point in which the Pallid Mask reveals himself to Queen Cassilda, the madness of Carcosa is unleashed into whichever hall the play is being produced (like, say, a Paris theatre).
In Chapter 61, Rony vaguely remembered that he may once have read the play, and believed Ulver Zandalus to have been speaking lines from it in Chapter 35 (Part 2). (“Unmask! Unmask! It’s time! It’s time!”)
The Yellow King explained to the party in Chapter 99 that he chose his name as a reference to this play. He described it as a taut political drama. He described the characterization of Queen Cassilda in the play in this manner: she seemed to be the hero of the story in Act I, then by Act III she appeared to be an anti-hero, and then by the end of the play she was revealed to be the “villain” of the piece. However, the Yellow King’s memory was compromised and he processed the act of working to thwart Hastur as a bad thing.
In Chapter 103, Vik looked at the wild party happening in Viscount Pietro Brellin‘s estate and it rang a bell in his head, reminding him of what little he remembered of the play.
First Reference: Chapter 13
Other Notable References: Chapter 35 (Part 2), Chapter 61, Chapter 99, Chapter 103