'Spencer' review: Kristen Stewart gives the performance of her life as Diana Spencer

It’s not a biopic. You should know that about “Spencer,” only in theaters, in which LA-born Kristen Stewart gives the performance of her life as Diana Spencer, Princess of Wales. Oscar should smile on Stewart, who makes “Spencer” a spellbinder from first scene to last.

Just don’t expect Diana’s full story. “Spencer” offers only 72 hours in the tumultuous life of the People’s Princess as she’s about to celebrate Christmas 1991 at Sandringham with the royal family and Prince Charles (Jack Farthing), the cheating husband she wants to kick to the curb.

That’s not so easy. Living in the Windsor pumpkin shell has driven Diana to mental collapse, worsened by her self abuse through cutting and bulimia. Diana would willingly disappear were it not for her young and adoring sons, William (Jack Nielen) and Harry (Freddie Spry).

For Chilean director Pablo Larrain, whose “Jackie” won an Oscar nomination for Natalie Portman in the role of JFK’s widow in the turbulent period just after his assassination, this tightly focused cinema snapshot becomes a cracked mirror into a woman’s soul.

Working from a dream-like script by Stephen Knight, Larrain imagines Diana from the get-go as lost. Literally. Having defied tradition to drive herself (no security) to the country manor of Queen Elizabeth (a rigidly chilly Stella Gonet), she stops at a café to ask, “Where am I?”

When she arrives late—another form of rebellion—Diana is told to dress as ordered, but not before getting on the scales. It’s a Victorian ritual in which guests are weighed going in and out to make sure they’ve put on pounds after the holiday in tribute to the nonstop, royal feasting.

Wait, it gets worse. Servants examine Diana’s pillow for hairs that might belong to a secret lover. Her bedroom curtains are sewn shut to foil paparazzi. Royal disapproval falls so heavily on Diana that she imagines herself as Anne Boleyn, the beheaded second wife of Henry VIII.

With in-house spies monitoring her every move for the crown or to sell her out to the media, Diana finds warmth and playful companionship with her dresser, Maggie, a small role given size, scope and genuine feeling by the great Sally Hawkins. But Maggie is soon sent away, leaving military man Alistar Gregory (a standout Timothy Spall) to keep Diana in line. Or else.

Other Dianas, from Emma Corrin and Elizabeth Debicki in “The Crown” to Jenna de Waal in Broadway’s “Diana: The Musical,” paint their portraits of Diana on a larger canvas. But Stewart‘s three-days-in-a-life interpretation is beyond compare and tellingly, thrillingly alive.

Without flashbacks or a mansplaining script, Stewart nails every nuance as Diana wanders the estate where she grew up as a carefree child in a rental house, now boarded up and full of ghosts to remind Diana of her once unscrutinized bliss as part of the Spencer family.

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Stewart, 31, knows the fame drill, having been a tabloid princess since her teen idol days as the star of the “Twilight” saga. That popularity probably influenced the snob Academy to ignore her stunning work in “Clouds of Sils Maria,” “Personal Shopper” and “Seberg.”

But there is no ignoring the Stewart tour de force in “Spencer.” The technical demands of the role from strict posture to posh accent are absorbed into an intimate and indelible portrayal that finds the grit, grace and grieving heart of a caged spirit.

What starts as an emotional horror show ends as the best jailbreak movie since “Shawshank.” There’s nothing here of the car crash that tragically ended Diana’s life at 36 in1996. Instead, “Spencer” shows Diana in the revitalizing act of escape from her privileged prison. And thanks to Stewart’s brilliant, bittersweet, utterly transporting performance, we get to watch her fly.