It's 1954 and Francoise Sagan (Sylvie Testud), still in her teens, has become a literary celebrity overnight with the success of her first novel Bonjour Tristesse. Sagan is enjoying the high life with her close friends Jacques (Pierre Palmade) and Bernard (Lionel Abelanski), while spending her royalties on liquor, sports cars, partying and evenings at the casino. Sagan, a bisexual, enjoyed short-lived romances with lovers of both genders but in the sixties she made an effort to settle down, marrying American expatriate Robert Westhoff (William Miller). While the two had a child, Westhoff's frequent homosexual affairs damaged their relationship beyond repair, and her longest-lasting romantic partnership was with Peggy (Jeanne Balibar), an editor at a fashion magazine. While Sagan continued to write, her appetite for alcohol and cocaine grew dramatically, and as her addiction became stronger, her literary output shrank and after years of failing to pay her taxes, she became dependent on the generosity of friends to survive and became a stranger to her only child.

Biopic blues befall another icon.

Note to science buffs: this picture is about the life of Francoise Sagan, the post-war French novelist, as opposed to Carl Sagan, the American astrophysicist and author. Still, this strange, bird-like woman, played with much fluttering of hands and defiant ignorance of simple truths by Sylvie Testud, could have done with some rational examination. As it is, veteran French filmmaker Diane Kurys’ biopic falls into the usual trap of being episodic without ever drawing a resonant whole from the piecemeal timeline. To reference the other Sagan, this movie is something of a black hole.

Then again, it wasn’t conceived as a movie. It originally screened on French television in 2008 as a two-part mini-series, running at 180 minutes. The ever industrious Luc Besson saw it and purchased the cinematic rights, instigating the trimming of an hour and banking on Francophiles to turn out for the story of a 1950s icon. Without seeing the television cut it’s hard to say whether Sagan has been improved or worsened, but the translation certainly presents problems: certain shots, especially outdoors, haven’t been well served by the technical transfer, and per episodic television the compositions tend to favour mid-distance group shots. The delicately sharp angles of Testud’s face are rarely examined in close-up by the camera.

The narrative does without that mainstay of the biopic, the formative childhood scenes. When we first meet Sagan she is a blithely ambitious 18-year-old who has just sold her debut novel Bonjour Tristesse. The solidly upper middle-class daughter of mercantile parents, Sagan’s story of an indolent playboy and his manipulative teenage daughter mixed wealth, teenage ennui and existential despair was catnip to 1954 readers. Within a book signing and an awards ceremony she’s a national icon and a millionaire to boot.

The famous description of Sagan was that of a 'charming little monster", from Le Figaro, and it defines the characterisation. Sagan picks up every tab and gambles extravagantly, drawing a circle of lovers and confidantes – generally one and the same – who she values as distractions but will brook no opposition from. She’s tempestuous and lucky, she takes risks and others pay the price. But it’s never clear why, as she’s essentially the same person at age 18 as at 69, when she passed in 2004. Her own writing dots the narration, but it’s little more than decorative.

Certain events suggest either her stupidity or an implied cruelty in the truncated storytelling. No sooner has she been charmed by her future middle-aged husband, Guy Schoeller (Denis Podalydes), on a promotional trip to New York, than he takes her back to Paris and turns into a contemptuous adulterer who strides around the house in riding breeches, barking insults. (He reminds one of Otto Preminger, who directed the 1958 screen adaptation of Bonjour Tristesse with David Niven and Jean Seberg, which isn’t referenced in this work.) Her second husband, who fathers Sagan’s eventually estranged son, brings his male lover to live with them. It’s difficult to offer anything but an indifferent shrug as Sagan ages, takes up cocaine, falls into debt (to the 'IRS", a somewhat craven translation for an American audience) and grows ever lonelier.

'How I destroy myself is my business" she announces as the bad times roll on, but her dissolution is presented as nothing more than a respite against boredom. Aside from various lovers such as Bernard Frank (Lionel Abelanski), there’s no connection to French cultural life, and interesting ideas that are aired aren’t maintained. Watching the historic student protests of 1968 at her country villa, drink in hand, Sagan begins to wonder if she is the voice of a now bypassed generation, but the script rarely worries about her place in the world, instead matching her selfish pursuit of a home life that provides her with de facto care. It’s the standard cautionary tale of the promising talent who is destroyed by getting what they want and it has to be done better than this to even remotely stand out. Ho hum.