Though part of her family had the membership, Brooke herself wasn't part of the New York branch of the Hellfire Club. Not since becoming her father's Red Rook under the London Branch. But as a prominent New York socialite, Brooke was very much invited to this event. (There was also the fact about Sebastian's return...)

So there she was, in an outfit carefully chosen to represent all three houses under the club, with a flute of sparkling sweet red wine in her hand, her eyes seeking out Stephanie, who she knew would most certainly be present.