1936's "Charlie Chan at the Opera" found Hollywood's resident monster Boris Karloff forsaking a vacation in his native Britain for filming at Fox in mid Sept.-mid Oct. Under the direction of H. Bruce Humberstone, 13th of Warner Oland's 16 entries in the popular series. Boris was no stranger to the Chan character, as he and Chan both made their talkie debut in equally miniscule roles in 1929's creaky Warner Baxter vehicle "Behind That Curtain," but here he enjoys second billing behind Oland as the amnesiac opera singer Gravelle, his singing voice dubbed by Tudor Williams, Oscar Levant composing the opera "Carnival" especially for the film, William Kernell writing the words in English before being translated into Italian, Boris required to don a costume of Mephistopheles designed for Lawrence Tibbett from the just completed "Under Your Spell." After wasting away as a sanitarium charity case for many years, his baritone often displayed at the piano, Gravelle suddenly recovers his memory after spotting a photo of his wife in the local paper, Lilli Rochelle (Margaret Irving) guilty of conspiring with her married lover, Enrico Barelli (Gregory Gaye), to rid themselves of her husband by locking him in his dressing room during a blazing theater fire. Chan becomes involved when Lilli and Enrico require police protection from a death threat against her as both are about to perform that night, their humiliated spouses topping the list of suspects, Frank Conroy as Mr. Whitely warning the baritone to keep away from Lilli, and Nedda Harrigan as Enrico's long suffering Anita Barelli, working behind Lilli as second soprano. Stalking the opera house is Gravelle, long believed dead by those involved, determined to usurp Barelli in his cherished role of Mephisto, scaring the daylights of the wardrobe mistress (Hilda Vaughn) but not deterring stage manager Mr. Arnold (Maurice Cass): "this opera is going on tonight even if Frankenstein walks in!" His performance goes on without a hitch, but Madame Lilli faints dead away as he brandishes his knife, both her and Enrico found stabbed shortly afterwards with Whitely inadvertently handling the murder weapon hidden in a bouquet of flowers. As was usually the case with Oland, Keye Luke as son Lee Chan offers up some lighter moments but is genuinely helpful and intelligent in his father's investigation, and would later replace Karloff for the 1940 Mr. Wong finale at Monogram, "Phantom of Chinatown." The much anticipated 'Warner Oland vs. Boris Karloff' showdown arrives at the 52 minute mark, Gravelle lamenting that his teenage daughter Kitty (Charlotte Henry) doesn't remember him, the crafty Chan biding time to keep him calm with one of his famous Chinese proverbs: "madness twin brother of genius because each live in world created by own ego, one sometime mistaken for other." Karloff's actual singing voice would not be heard until roles on Broadway and television, happy to keep busy during what was destined to be a rough patch of non horror vehicles that gave him star billing yet would be quietly forgotten once Universal revived the genre with "Son of Frankenstein." Oland would only live long enough to complete three more Chans before his untimely death at age 58, Sidney Toler gamely carrying on in 22 before Roland Winters closed out the long running series in the final six.