When people say Meryl Streep is a great actress, they mean grand actress one who calculates her moves, her makeup and her accent, and then turns up the thespic volume until her character risks becoming caricature. The tactic works when she plays Dragon Lady roles like the fashion doyenne in The Devil Wears Prada, less so in the more naturalistic settings of Mamma Mia! and Doubt. But given a famous woman to play, Streep eerily locates the voice, face and soul: of Julia Child in Julie & Julia and, with startling acuity, of Margaret Thatcher in this biopic. Smartly written by Abi Morgan (who co-wrote Shame) and directed by Mamma Mia!'s Phyllida Lloyd, the film spans nearly the complete life of Britain's first female Prime Minister, from her youth as a greengrocer's daughter through Oxford and her early years in the Conservative Party (when she is played by Alexandra Roach). Streep takes over in Maggie's middle age and escorts the PM into a restless retirement, both haunted and warmed by the specter of her late husband Dennis (a marvelous Jim Broadbent). Her performance is a miracle of inhabiting, not editorializing; it turns the boss of 10 Downing Street into a woman meriting our sympathy and sadness. This time, grand is great.