Yet as soon as their honeymoon in Jamaica begins, Rita does not act like herself. She adopts a hearty tourist swagger, loses her social conscience, gives up drinking and salt, and astonishes Peter by announcing she wants to have a baby-just what she’d said she didn’t want. Who the hell is this stranger he’s just married?

Anyone who’s seen Craig Lucas’s Prelude to a Kiss onstage knows the supernatural answer. For this is a contemporary fairy tale that takes the old magical rules, in which princes can be transformed into frogs or beasts, and transports them into the anxious modern world, where AIDS and other horrors have given the link between love and death a new urgency.

What’s happened to Rita (skip this paragraph if you want the movie to surprise you) is that she has swapped souls with an old man (Sydney Walker), the result of a mysterious kiss he plants upon the bride at her wedding. Rita’s soul is now walking around Chicago, lovesick for Peter, in the body of a decrepit, cancerous old gent. He, meanwhile, is happy as punch to be reborn in her blond, firm young body-and he’s not about to let on to “her” new husband what’s happened. Peter is going to have to figure it out himself, and figure out a way to get Rita’s soul back in its proper place.

It’s a novel, and zany, romantic dilemma, and though Lucas gets plenty of laughs out of this preposterous situation, what’s singular about " Prelude to a Kiss" is the depth of feeling it wrests from this whimsical conceit. Though the movie is not about AIDS (unlike the previous movie collaboration between Lucas and director Norman Rene, “Longtime Companion”), it’s hard not to think that this deceptively slight romantic comedy was conceived in response to that disease, which, like a witch’s curse, can transform a young beauty into a physical beast. From the movie’s opening images of a clock tower and a watch, this love story gains poignance from the pressure of ticking mortality.

This is Baldwin’s finest hour since “Miami Blues,” and utterly unlike anything he’s done on screen before. His subtle, funny, heartfelt performance meshes beautifully with Ryan’s pugnacious neurotic charm. Ryan, however, may be a little too vivacious: when we’re told, late in the tale, that Rita’s problem is how to overcome her crippling fear, it doesn’t ring true. We haven’t seen the fear. Walker plays the old man with tact and sentimental restraint, and Ned Beatty and Patty Duke are richly funny as Rita’s oppressively supportive parents. With the help of a plaintive, well chosen soundtrack (Annie Lennox’s version of " Ev’ry Time We Say Goodbye," Van Morrison, Cowboy Junkies), “Prelude to a Kiss” has made the voyage from Broadway to Hollywood with its literacy, charm and full heart very much intact.