Emil Jannings as Professor Rath in Josef von Sternberg's The Blue Angel (1930) is possibly the most famous example of this kind of character as a movie protagonist. Rath, a puritanical disciplinarian, goes to a cabaret one night to catch his students there and ends up falling for Marlene Dietrich as the sleazy chanteuse they go to see. (He's particularly taken with a postcard of her with a glued-on skirt--you blow on it to expose her silk underpants.) He's so ludicrously upright he can't just sleep with her and lie about it. When confronted by his headmaster about his relations with her, he gets angry at the man for insulting his future wife. Rath loses his job, does marry her, works in the theater hawking those postcards, and loses his place in society, his self-respect, and finally his mind. The Blue Angel is an ironic romance in which surrender to lust is exactly the delusional trap the Professor would have said it was, but once he's aroused he has no defenses against it. It's a nightmare in which there's no stable resting point between abstinence (angel) and degradation (blue), an original sin myth in a world spent beyond the capacity of a savior to redeem it.

Sarah has some of the authoritarian quality of Professor Rath, especially when she assumes the character of a disapproving mother, but though she's taken with the sensual-louche Julie she stays in control--the hypocritical prig ascendant. Rather than being destroyed she's rejuvenated. There are isolating shots of Sarah looking through panes of glass at Julie, and then doubly reflected in mirrors typing away, but what she does to get the book written is, finally and unexpectedly, seen as a form of vitality. The movie shows writing as a creative act of psychological dissolution and reformulation, and Sarah may be a prude and a hypocrite and even at times a witch, but she turns out something we consider socially valuable, and thus is one of the few ironic protagonists who is actually a heroine. It's in that sense doubly ironic, first because the protagonist's distance from the ideal is never disguised, and second because those very quirks turn out, against expectations, to be central to what makes her a protagonist we can admire. Sarah returns to London looking restored, and you think, She's earned it. (We don't need the comeuppance to John. It makes it seem as though her problem had been simply a bad man, and that diminishes what we've seen. Nor do we require that the book be in a new, more emotional vein for her--"better" than a mere mystery.)

The movie is least satisfactory in the way it connects Sarah's fascination with Julie to her being specifically a mystery novelist. The scenes in which she engages in detection are no more than cursory and while Sarah's quirkiness does make her resemble a detective hero (someone like Agatha Christie's Hercule Poirot, who is also an oddity, even a figure of fun, and hence an ironic protagonist), Sarah is a larger conception and so you don't get much from this element of the script. Eccentric movie detectives don't have complicated personalities. However entertaining, they're functional figures who unravel their creator's knots and at most indicate how we feel about the goings-on they've investigated. Sarah is a more striking figure as writer than detective.