She was still sleeping when he left around daybreak. It was a crisp clear morning, and he set out to walk a few blocks and wound up walking all the way home. She lived in a loft on the top floor of a converted warehouse on Crosby Street, and he’d been living for years now in a prewar apartment building on First Avenue, just a few blocks up from the United Nations. He stopped for breakfast along the way, and he lingered in Union Square to look at the trees. Closer to home he ducked into a bookstore and flipped through a pocket guide to the trees of North America. The book was designed to enable you to identify a tree, and then told you everything you might want to know about it. More, he decided, than he needed to know, and he left without buying the book.

But he went on noticing the trees the rest of the way home. Midtown Manhattan wasn’t exactly the Bois de Boulogne, but most of the side streets in Kips Bay and Murray Hill had some trees planted at curbside, and he found himself looking at them like somebody who’d never seen a tree before.

He’d always been aware of the city’s trees, and never more so than during the months when he’d owned a dog. But a dog owner tends to see a tree as an essentially utilitarian object. Keller, dogless now, was able to see the trees as-what? Art objects, possessed of special properties of form and color and density? Evidence of God’s handiwork on earth? Powerful beings in their own right? Keller wasn’t sure, but he couldn’t take his eyes off them.

At home in his tidy one-bedroom apartment, Keller found himself struck by the emptiness of his walls. He had a pair of Japanese prints in his bedroom, neatly framed in bamboo, the Christmas gift of a girlfriend who’d long since married and moved away. The only artwork in the living room was a poster Keller had bought on his own, after he’d viewed a Hopper retrospective a few years ago at the Whitney.

The poster showed one of the artist’s most recognizable works, solitary diners at a cafй counter, and its mood was unutterably lonely. Keller found it cheering. Its message for him was that he was not alone in his solitude, that the city (and by extension the world) was full of lonely guys, sitting on stools in some sad cafй, drinking their cups of coffee and getting through the days and nights.

The Japanese prints were unobjectionable, but he hadn’t paid any attention to them in years. The poster was different, he enjoyed looking at it, but it was just a poster. What it did, really, was refresh his memory of the original oil painting it depicted. If he’d never seen the painting itself, well, he’d probably still respond to the poster, but it wouldn’t have anywhere near the same impact on him.

As far as owning an original Hopper, well, that was out of the question. Keller’s work was profitable, he could afford to live comfortably and still sink a good deal of money into his stamp collection, but he was light-years away from being able to hang Edward Hopper on his wall. The painting shown on his poster-well, it wasn’t for sale, but if it ever did come up at auction it would bring a seven-figure price. Keller figured he might be able to pay seven figures for a piece of art, but only if two of those figures came after the decimal point.

Keller had lunch at a Vietnamese restaurant on Third Avenue, then stopped at a florist. From there he walked up to Fifty-seventh Street, where he found a building he’d noticed in passing, with one or more art galleries on each of its ten floors. All but a couple were open, and he walked through them in turn, having a look at the works on display. At first he was wary that the gallery attendants would give him a sales pitch, or that he’d feel like an interloper, looking at work he had no intention of buying. But nobody even nodded at him, or gave any sign of caring what he looked at or how long he looked at it, and by the time he’d walked in and out of three galleries he was entirely at ease.

It was like going to a museum, he realized. It was exactly like going to a museum, except for two things. You didn’t have to pay to get in, and there were no groups of restless children, with their teachers desperate to explain things to them.

How were you supposed to know how much the stuff cost? There was a number stuck to the wall beside each painting, but there were no dollar signs, and the numbers ran in sequence, 1-2-3-4-5-6-7, and couldn’t possibly have anything to do with the price. Evidently it was considered loutish to post the price publicly, but didn’t they want sales? What were you supposed to do, ask the price of anything that caught your eye?

Then at one gallery he noticed another patron carrying a plastic-laminated sheet of paper, referring to it occasionally, dropping it at the front table on her way out. Keller retrieved it, and damned if it didn’t contain a numbered list of all the works on display, along with the title, the dimensions, the medium (oil, watercolor, acrylic, and gouache, whatever that was), and the year it was completed.

One work had NFS for a price, which he supposed meant Not For Sale. And two had little red dots next to the price, and he remembered that some of the paintings had displayed similar red dots alongside their numbers. Of course-the red dots meant the paintings had been sold! They wouldn’t just wrap one up and send you home with it. The paintings had to hang for the duration of the show, so when you bought something, they tagged it with a red dot and left it right where it was.

He congratulated himself for figuring it all out, then was taken aback by the thought that everyone else no doubt already knew it. In all the galleries in New York, he was probably the only person who’d lacked this particular bit of knowledge. Well, at least he’d been able to work it out on his own. He hadn’t made a fool of himself, asking what the dots were for.

By the time he got home the mail was in. Keller had never cared much about the mail, collecting it and dealing with it as it came, tossing the junk mail and paying the bills. Then he took up stamp collecting, and now every day’s mail held treasures.

Dealers throughout the country, and a few overseas, sent him the stamps he’d ordered from their lists, or won in mail auctions. Others sent him selections on approval, to examine at leisure and keep what pleased him. And there were the monthly stamp magazines, and a weekly stamp newspaper, and no end of auction catalogs and price lists and special offers.

Today, along with the usual lists and catalogs, Keller received his monthly selection from a woman in Maine. “Dear John,” he read. “Here’s a nice lot of German Colonies, plus a few others for your inspection. Enclosed are 26 glassines totaling $194.43. Hope you find some to your liking. Sincerely, Beatrice.”

Keller had been dealing with Beatrice Rundstadt for almost two years now. She enclosed a similar note with each shipment, and he always wrote back along the same lines: “Dear Beatrice, Thanks for a nice selection, much of which has found a home here on First Avenue. I’m enclosing my check for $83.57 and look forward to next month’s assortment. Yours, John.” It had taken well over a year of Dear Mr. Keller and Dear Ms. Rundstadt, but now they were John and Beatrice, which gave the correspondence a nice illusion of intimacy.

Just an illusion, though. He didn’t know if Beatrice Rundstadt was married or single, old or young, tall or short, fat or thin, didn’t know if she collected stamps herself (as many dealers did) or thought collecting stamps was a fool’s errand (as many other dealers did). For her part, all she knew about him was what he collected.

And that was how he hoped it would remain. Oh, he couldn’t avoid the occasional fantasy, in which Bea Rundstadt (or some other lady philatelist) turned out to be a soul mate with the face of an angel and the build of a Barbie doll. Fantasies were harmless, as long as you kept them in their place. His notes remained as steadfastly perfunctory as hers. She sent him stamps, he sent her checks. Why mess with something that worked?