China Miéville's 2009 novel, The City & The City, posits a world in which a similar skill is practiced by the entire population of two neighboring cities, Besźel and Ul Qoma, in what seems to be Eastern Europe.
At one level, The City & The City is a murder mystery, a noir-ish police procedural narrated by Tyador Borlú, an inspector in the homicide division of the Besźel police. He's investigating the murder of an unknown woman whose body has been dumped in an empty lot. In the course of his investigation, he must deal not only with his colleagues and the criminal element in Besźel, but with other interested parties: his counterpart in the Ul Qoma police force; archaeologists exploring a mysterious, extensive dig in Ul Qoma; the governing body -- The Committee -- which oversees relations between the two cities; and the shadowy and apparently all-powerful agency known simply as Breach.
At another level, the book is a dark urban fantasy. No -- no magic-users and mythical species here. What makes the world of Besźel and Ul Qoma a world of fantasy is a single, enormously weird feature: the two cities are (as Borlú says) geographically distant... but occupy the same geographical location: physically overlapping, yet functionally separate.
(It's like the opposite of that old Gertrude Stein quip about Oakland: in both Besźel and Ul Qoma, there are always two theres there.)
No one knows how this came to be. They know only that long ago, either a single city split into two, or two separate cities became somehow co-located. The event is known as Cleavage -- cleverly, one of those words which means both something, and its opposite. (And yes, British Miéville's protagonist acknowledges the unfortunate coincidence with the American slang term.)
What these people do know is that legally, they may be in only one city or the other. They may stand in Besźel, say, and from there they can look at and see Besźel... but not Ul Qoma, although they can sense it out of the corner of their eye, so to speak. Citizens of each city have trained themselves to unsee the citizens, buildings, and roadways of the other. (Importantly, this is a learned mental unseeing, not a physical one. Driving in one city is nerve-wracking, because drivers must avoid pedestrians and other vehicles in both cities.) Moving from one city to another by any means other than the most tightly controlled is a crime even more serious than murder, called breaching.
And breaching is dealt with swiftly, irrevocably, finally by the ever-watchful Breach...
You now understand, I hope, why I opened this review with all that about eyeglasses. On one hand it sounds strange -- impossible -- that two worlds should overlap so completely, yet be able to be "seen" separately; on the other, it's perfectly natural -- just a matter of training your eyes. (There are even blurry zones, not completely in one city or the other, called "crosshatches.")
I don't want to dwell too much on this device, lest I ruin someone else's pleasure in discovering the nuances for themselves. I will say, though, that Miéville has done an amazing job of working this all out. A good thing, too: the murder which Borlú investigates was committed in Ul Qoma; the body was then moved to Besźel. Imagine trying to understand geographic clues if the author had only a loose grip on his own gimmick.
That word "gimmick" raises an important question, though. Imagine The City & The City without it; does the book still work?
I think the answer is yes. Miéville's prose does just what you want the prose of a contemporary police procedural to do: explain clearly (and within the limits of first-person narrative) what Borlú and the other characters are up to; trigger empathy for the protagonist (and those he comes into contact with, however different they are from one another); give the detective amazing, but not too amazing, deductive powers; match mood and rhythm to the exposition or action of a given paragraph or scene; and lead to a satisfying cluster of conclusions (both for the characters, and for the mystery itself).
Yet the unique premise allows occasional small flourishes of language like this one, describing a park where foreign archaeological students working on that dig take their leisure -- and push the limits of what the no-breaching laws allow:
Maps made clear to walkers where they might go. It was here in the crosshatch that the students might stand scandalously, touching distance from a foreign power, a pornography of separation.Finally, I imagine yet another possible reading of The City & The City: as a metaphor for real cities, inhabited by multiple classes and populations who carefully refrain from interaction. That might justify a second review, or a third. But this one is already long enough: let's just agree to unsee that other possibility for now.