Have you ever wondered what your life would be like if you hadn't taken a particular trip, met a certain person, or gone to a specific party? Sliding Doors explores that question for Helen, a London public relations executive played smashingly by Gwyneth Paltrow. After being fired from her job, she misses the subway home. Or does she? This fascinating movie shows what happens to Helen -- and her love life -- in both cases.

By catching the train, she meets a handsome stranger (John Hannah) who becomes infatuated with her. But she also arrives home early to find her live-in boyfriend (John Lynch) in bed with a former girlfriend (Jeanne Tripplehorn). Conversely, by missing the subway, Helen falls victim to a mugger and doesn't get home until her boyfriend's tryst is over.

A remarkable depiction of parallel universes emerges in this provocative movie. It's done with great style, humor, and heart -- thanks to first-time director Peter Howitt. Looking more like a football player than a filmmaker, Howitt confesses feeling relieved that viewers can follow his film's intertwined stories. "It took me three years of writing and twenty drafts of a screenplay before getting it right, and I'd still like to film the whole thing over," he explains.

Describing the incident that inspired his movie, Howitt recalls needing to make a phone call on a day while walking on a busy London street. "I wondered if I should wait until I got home or use the callbox across the street. I decided to call right away, stepped into the road, and was almost hit by a car." This close call jolted the filmmaker's mind. He became obsessed with how his life might have been different had he been hit. "The idea bugged me for ages, but it was four years before I started writing the screenplay," he declares.

For me, it was very easy to follow Paltrow's character through her two worlds.  One Helen cuts and bleaches her hair and becomes more liberated as she takes on a new career. The other Helen, the one who stays with her lout of a boyfriend, comes across as much more shy and vulnerable. Because of Paltrow's incredible ability to draw me into her performances, I was captivated by both versions of the character she portrays. And I desperately wanted this lovely woman, whichever one she really was, to end up with the amusing stranger she met on the subway. No doubt about it: he's definitely more fun, especially when he quotes those hilarious Monty Python bits.

Sliding Doors raises questions about fate and the mysteries of life. I like to call it "a thinking person's romantic comedy." But, hey, don't let that frighten you away. It's also entertaining and lots of fun!

(Released by Miramax/Paramount Pictures and rated "R" for some sexuality and language.)