A movie, or at least a memorable one, tends to be about the inner lives of its characters. In too many films today, though, the characters have inner lives that are thin, scannable, mystery-free. But Pablo Larraín’s entrancing drama is a lightning rod that channels the inner life of Princess Diana — the jolt and sparks of anxiety and melancholy that have turned her, during a Christmas weekend with the Royal Family, into a Royal Nervous Wreck Without a Cause. Kristen Stewart, transforming herself, does a tremulously acerbic and precise recreation of the Di personality (the halting elegance, the shyness jostling with the coquettishness of fame). But that’s just the ground floor of her performance. She takes the audience on a flesh-and-blood journey in a movie that’s at once a diary, a soap opera, a horror film, and a rigorously speculative drawing-room biopic. It’s a much more close-up experience than “The Crown.” It is also, at moments, like “The Shining” rewritten by Edith Wharton. Di, for all her privilege, is trapped in a dead marriage that makes her feel like a caged bird, and since that marriage is part of England’s infrastructure she thinks there’s no key. She finds it on the hunting ground, in the most moving scene in any film this year. She frees herself and, in doing so, rocks the old world order. “Spencer” is a tale of despair and transcendence that celebrates the true meaning of being royal.