In that seemingly endless British sci-fi TV series, "Dr. Who," the various incarnations of the good doctor travel through time and space with the use of a machine that is, basically, a nice red British telephone booth. I suppose that fit the budget of the BBC, but if the producers wanted to be more believable, they'd have sprung for a mock-up of a train car from the Tube, London's justly famous underground rail network. I ride the Tube faithfully every time my wife and I visit London, and it always seems magical to me.

Oh. I've ridden other light rail, and I've liked most of them. But some of those that rival the Tube in extent and thoroughness, like New York and Chicago, spend a lot of time aboveground even as they speed through key areas. And most others have a relatively trifling number of stops and a very limited set of routes.

None, in my eyes, can compare with the Tube. You walk down into a hole in the ground and emerge 15 minutes later somewhere entirely different. Magic.

There's more, of course, to the Tube's allure. How about the way it turns people into a synchronized mechanical ballet, something like those Rube Goldbergian toys where you construct a maze of chutes, tracks, teeter-totters and such and then send marbles clattering through? When you descend into a Tube stop, you first slide your ticket through and click past a turnstile. Then it's a few steps to a long, steep escalator and through tunnel after bending tunnel, up stairs, down stairs, up ramps and down, around curves, with directional signs suddenly ordering you to abruptly split off from the main path and duck through a side passage into a completely different part of the maze. The spectacle is best at rush hour, with streams of passengers blending together, flowing apart, occasionally pouring into one big chaotic Brownian motion swirl and miraculously coalescing again into separate streams. In some stations your path will from time to time run parallel to another, separated now by a row of low fences like misplaced bike racks, then by long stretches of wall pierced by regularly spaced side passages so that you see your ghostly companion stream only in jerky snatches like an old silent movie.

And the Tube is special because it intensifies the feeling an American -- well, at least this American -- gets that England is actually a mirror USA, something from that alternate Earth on the other side of the Sun in the Superman comic books. In aboveground London, the un-American artifacts are overwhelming. And there's a confusing admixture of very American items, like a corner McDonalds. Underground, the environment is much more Spartan, no neon signs or blinking digital come-ons, just a few posters on clean tile walls. That seems to hammer home the unfamiliarities -- the odd word on an ad that certainly looks like English, but doesn't mean anything to American eyes. Or the candy machine stocked with brands you've never heard of, next to a drink machine selling only boxes of something called Ribena. What's a blackcurrant? Why do the same flavors show up in regular and "toothfriendly" versions? In this world, does green kryptonite make Superman stronger?

Sorry if I'm getting too weird for you. The Tube can do that -- because it transports you to another world.

It's a world with no national boundaries. Sit on the Tube for just a few stops and you'll hear German, Japanese, French, Spanish, Russian. Maybe even a little English. You'll see olive-skinned men with big, bushy moustaches; tall, blonde ice queens with cheekbones that could scribe glass; skinny Asian guys with that weird Ken-doll stiffness; what presumably are women wrapped head-to-toe in a rainbow of silks with coal-black eyes peering through a narrow slit.

On this particular night, it was a blend of Third World and First that caught my eye.

My wife and I were coming back from the theater -- one of those no-pretensions-to-artistic-merit musicals cobbled together from somebody's light-rock greatest hits album. Several other shows had let out at the same time, and even though we weren't on one of the busiest lines the car was still full. My wife and I got the last two seats -- her on the outside of a forward-facing bench, me just behind her on one of the solo seats facing into the car just by a set of doors. You're supposed to give up those seats to old folks, people with disabilities, pregnant women and such. There were a couple of standees at either end of the car, but they looked to be quite healthy teens so I sank into the seat with no guilt and a good measure of relief. We'd been on our feet all day. The play was a welcome rest, but it had ended with a 20-minute encore of the most well-known of the show's songs, pulling the whole audience to its feet for a stomping, swaying celebration. Then there'd been the crush of the various theater's crowds forming rugby scrums we had to struggle through. And there was some kind of security alert at the station -- with the several diehard IRA factions, it seems there's always some kind of threat. This one had, for no apparent reason, shut off power to the station's lifts. Lacking the usual escalators, that meant a long spiraling journey down a cramped staircase. My wife and I were both pooped by the bottom. When the train pulled in, we fell into the seats. I tapped her on the shoulder; she turned toward me briefly and smiled and we settled in for the short ride to our hotel.

That's when I began to scan the passengers around me. It was the usual eclectic collection, but just one woman intrigued me.

She was sitting across the aisle from my wife. Her skin was the polished brass of an East Asian -- to me, always the most exotic and tantalizing women; it seems as if you can taste the curry and other spices when you see their glowing skin. This woman couldn't have been more than 5'3 or 5'4, all in perfect proportions. She had a round, open face, small features except for long, arched brows etched above wide olive eyes. Elegant gold filigrees hung from her long, delicate, almost translucent ears. Jet-black hair with a few shiny silver strands cascaded in gentle waves to her shoulders.

Her gently sloping hourglass frame was encased in an exquisitely tailored dark green suit cut just above the knee, but with a slit on the side that had fallen open to expose a few square inches of smooth thigh. That led down to a perfectly curved pair of legs in sheer hose, ending in three-inch-high spikes on the butter-soft leather pumps that matched the forest green of her suit. The V-shaped opening of her white blouse showed no cleavage, but it did lay bare the chiseled collarbone from which sprung a taut neck of elegant length.

All in all, the picture of a modern businesswoman. But there were two things that didn't fit, two things that held my attention, two things that took me out of London and transported me to a faraway land.

One was her lips. Full, but proportioned to her small face, they glistened with a rich, dark wine-red hue that spoke of sinuous passageways to crowded bazaars, of harems full of beautiful women. I had never seen a color like that before.

But there it was -- not only on her lips, but also in the dime-sized circle rubbed into her skin precisely between her eyebrows.

Her lush lips could have been some makeup maven's fevered inspiration, but that dot was the pure mystery of the East. To see it on someone clothed in the uniform of the working West heightened the attraction.

I tried not to stare, but my eyes kept returning to this woman's exotic beauty. A time or two I thought she might have sensed someone watching her, because she turned around and scanned the people behind her. But I always slid my eyes off her in time to escape detection, as far as I could tell.

A couple of stops into our trip, the lights flickered briefly as we left a station. My wife turned to me in alarm; I reassured her; she's afraid of the dark. She put her hand back and I reached out to hold it. As I did so, I looked up and found the woman across the aisle looking right at me and smiling. And I could have sworn she winked.