MY MOTHER has never liked movies with costumes in them -- they tend to be stiff and drafty and everybody gets beheaded. "Lady Jane" is that sort of movie, a classy, luxurious-looking costume drama with castles and bloomers and hats that look like plumped-up pancakes. There are tall hounds with their noses turned up as high as the royal folk who ride about hunting things.

But mom might want to give this one a chance.

Trevor Nunn, the Royal Shakespearean who directed "Cats" and "Nicholas Nickleby," moves handsomely into feature films with this formal romance, a tragic tear-jerker set in Tudor England during the nine-day reign of 16-year-old Queen Jane.

An aristocratic newcomer, Helena Bonham Carter, with a face off a cameo and the bearing of a nun, plays the studious and unfortunate Jane Grey, a devout, cloistered girl who is forced into a political marriage to a 17-year- old hedonist named Guilford Dudley.

Newcomer Cary Elwes, big, blond and hunky, is the rowdy, rebellious Dudley whose father arranges the marriage as part of a plan to prevent Mary, a Catholic, from inheriting the throne. Jane and Dudley are set up as monarchs instead.

This true story offers all the passionate trappings of a modern teen romance, in which this dramatically mismatched pair overcome their initial resentment to embark on one of history's most idealistic love affairs.

Jane's mother, the Mommy Dearest of the 1550s, beats Jane into accepting the proposal and pushes her onto the throne. But the stubborn new queen and her consort, no longer pawns, rock the aristocracy with populist edicts, paving the way for Mary's grab for power. The two are arrested by Mary's forces and after eight months beheaded at the Tower of London.

Unfortunately it's sometimes rather silly, as when the future queen throws a tantrum at her crowning: "I won't. I won't," she whines -- a royal pain. Despite these lapses in decorum, "Jane" makes an impressive Tudor "Romeo and Juliet," full of pomp and circumstance.

LADY JANE (PG-13) -- At the K-B Janus.