In the sixteenth century, Queen Elizabeth I (Florence Eldridge) learns that MaryStewart (Katharine Hepburn) has returned to Scotland to take her throne, while refusing to yield her claim to England. The Scottish lords, under the lead of the treacherous James Stewart, Earl of Moray (Ian Keith), have been using the fanatical preacher, John Knox (Moroni Olson), to defame Mary as a dissolute persecutor. Mary finds support in the person of the bluff Earl of Bothwell (Fredric March), with whom she falls in love, but, angered by his presumption and urged by her Catholic secretary David Rizzio (John Carradine) to marry a Catholic, to strengthen her claim to the English throne, she weds the drunken, effeminate Lord Darnley (Douglas Walton). Darnley, despised by all and insanely jealous, conspires with the lords to murder Rizzio. Thereafter the lords blow up (no, really) the feckless Darnley and seize Mary and her infant heir, James VI. She escapes to Bothwell, who "forces" her to marry him; denounced by John Knox, Bothwell agrees to leave Scotland, so long as Mary is left on the throne. However, as soon as he is gone, the lords betray her. Mary escapes to England, seeking aid from Elizabeth -- who instead imprisons her. She is tried for conspiracy against Elizabeth; having heard meanwhile of Bothwell's death in prison, she accepts her condemnation to death. Elizabeth comes to her secretly to offer a last chance if she will renounce her claim to the throne, but Mary rejects her offer, taunting the English queen with her loveless life and the fact that Mary's son will inherit Elizabeth's throne. She then goes to her death -- hearing as in a vision the pipers of Bothwell announcing her apotheosis.