I, Tonya brings us a dizzying routine of fire and ice.

Trashy, foul-mouthed, blessed with talent and a wild, impetuous, unpredictable streak, “I, Tonya” is a mirror image of its troubled subject, notorious American figure skater Tonya Harding.

Craig Gillespie’s capricious, powder keg biopic takes us on a whirlwind tour through Harding’s life from her burgeoning talent as a youngster to her rise and fall as America’s Bad Girl sweetheart.

Gillespie’s weaves together disparate strands of familial vindictiveness, guileless talent, outrageous farce and period detail together into a propulsive narrative that scarcely pauses to draw breath. The cod-documentary style – ‘interviews’ interspersed with recreations and the occasional fourth-wall break – is a mixed blessing. It’s tremendously entertaining and allows for some superb comic moments to punctuate the blackly farcical tragedy that slowly unfolds but it also lends the film a patchwork, uneven quality and a tendency to risk narrative whiplash as it pirouettes wildly from smart mouth whimsy to vicious, brutal violence, not always sticking the landing.

It keeps it balance thanks to a pair of powerhouse performances from Allison Janney as LaVona Golden, Harding’s mother and, of course, Margot Robbie as Tonya herself. Margot Robbie’s screen charisma keeps the audience onside for Tonya even as her behaviour and choices seek to turn you against her but its Janney’s viscerally callous matriarch who forms the eye of the perfect storm of greed, cruelty and stupidity which enveloped and consumed Tonya and any chance to make the most of the talent she had.

It never seeks to excuse Harding’s flaws, only explain them and provide the emotional context for her public persona and the events which unfolded. There’s something of a disconnect between what it shows of the behaviour of husband Jeff Gillooly (Sebastian Stan) during their marriage and how it treats the character in the ‘present day’ segments and a bizarre series of cameo vignettes from Bobby Cannavale as Martin Maddox, a television producer distract more than inform, ultimately meaning the finished film is markedly less than the sum of its parts. Nonetheless, it’s a sparky biopic with some great performances and a kicking soundtrack, even if it is a little too obviously keen for “Guardians Of The Galaxy”-style breakout success.