“Spencer” (Diana’s surname, for any who have forgotten) takes off in speculative ways based on a real moment, when Diana spent Christmas weekend with the Royals at the Queen’s Sandringham Estate as her marriage to Prince Charles (Jack Farthing) was crumbling. Arriving late, she’s alternately depressed and defiant, well aware that all eyes are on her even before being warned that the press is “circling us.”

The dissonant music thus becomes a proxy for what’s going on inside Diana’s head (some of her long walks down the hall bring to mind “The Shining”), as she reads a book about the ill-fated Anne Boleyn and wonders whether she could wind up on the chopping block. She also is dealing with bulimia, to the point where the chef worries about her meals and Charles asks her not to purge them.

Diana’s rebelliousness catches the eye of a starched bureaucrat (Timothy Spall) who is there to keep an eye on her and mitigate potential harm to the family. The most sympathetic presence, meanwhile, is Diana’s dresser (Sally Hawkins), who doesn’t bat an eye when Diana tells her an outfit “doesn’t fit my mood,” and assesses her position vis-à-vis the Royal Family by saying, “They can’t change. You have to change.”