A microcosm of secrecy, high-society, and spookiness mingles behind a black gate, warning voie privée (private road) on Avenue Frochot in Pigalle. This dead-end street, inaccessible to the public, hides fairytale neo-Renaissance villas behind wisteria trees and rose bushes. Marked by an elaborate stained glass window of an old 1930s cabaret to the left of the entrance,…