Describing the beginning of Demon's affair with Marina, Van Veen (the narrator and main character in VN’s novel Ada, 1969) mentions Baron d'O. (or Baron O., a character in the stage perfomance in which Marina played the heroine) who strolled out of a side alley, all spurs and green tails:
Marina’s affair with Demon Veen started on his, her, and Daniel Veen’s birthday, January 5, 1868, when she was twenty-four and both Veens thirty.