The director’s obsessions with his female stars (Ingrid Bergman, Grace Kelly, Vera Miles, Tippi Hedren) must count as especially well-trodden ground by now, after two 2012 screen treatments — Hitchcock and The Girl — which broached the topic. Ackroyd makes a valid and rarer point about the leitmotif of homosexuality in his films. “It would be an interesting parlour game,” he writes, “to name any of his principal characters who were not intimated to be bisexual.” We’d go further with the two killers in Rope (1948), the cross-dressing culprit in Murder! (1930), Norman Bates in Psycho (1960), Martin Landau’s henchman in North by Northwest (1959) and Bruno in Strangers on a Train (1951) — which Ackroyd stops short of pointing out.