The diner is a thing of beauty, an American institution. It is there for the road-weary traveler, the night-shift worker, the gaggle of teenagers, the hungover mornings after. By the side of the highway, in the heart of the city, wherever it is needed (or so it used to be), the diner serves the simple things—a cup of joe, a hamburg sandwich (as they used to call it), a slice of pie. A diner needn't be great, only good.

A diner that is too good necessarily ascends out of its class. Think of Skillet Diner on Capitol Hill—its slick meta-diner interior and its "Deconstructed Corned Beef Hash." It is more than a diner, with its local ingredients and concomitantly higher prices, its patrons talking about their 401(k)s or latest graphic design project. It is also, somehow, less than a diner—less than what we see in the movies in our minds when the characters walk in and sink onto their stools or into their booth, with love or murder or the dropping out of beauty school on their minds.

To make a new diner in the classic mold is an undertaking to be handled with care. You do not want to stray into nostalgia overdose (though many do, if not most). You do not want to appear to be trying too hard in any direction, for that is not the spirit of the diner, which is utilitarian, kindhearted, tidy. The new Square Knot Diner in Georgetown has hit the nail squarely on the head. Here is the hexagonal tile, black and white. Here is the horseshoe counter with the swivel stools with backs on them for comfort and new upholstery, but cheerful chips in the paint of the base. Here is a sign advertising "BACON N' EGGS" with a happy pig and chicken, illiterately oblivious to their own fate. The diamond-patterned metal panels behind the humming old-fashioned double-doored refrigerator are just right; the dark-stained wainscoting needs a little wearing-in, which is so much better than if it were calculatedly pre-distressed. The radio plays classic rock. The curious-once-you-notice-it pulley-thing up above is left over from when the space was used to make parts for Boeing, just down the road. Out the windows, across the street, the stolidly lovely "GENERAL OFFICES" of the old Rainier Brewery sit in immovable brick; past it, a train goes by from time to time. The Square Knot adjoins the 9 Lb. Hammer, itself a paragon of its bar type.

The Square Knot makes a fine cup of coffee, strong but not too strong (I don't know what kind; this is not a question to ask at a diner). The hamburger is notably juicy, easily in the upper 20th percentile of diner burgers. They don't ask you how you want it cooked, they just cook it right. The fries are of that diner style that's uniformly golden but not exactly crispy—serviceable. The sandwiches (e.g., a Reuben and a tribute to Thanksgiving with turkey and cranberry) are home-style, if someone at your home makes good sandwiches; they're not overstuffed with meat, made plain and pleasing. A large ramekin of potatoes au gratin (available as an alternate to fries), while nicely cheesy, contained potatoes on the al dente side; a Jamaican lentil soup's veggies, however, were not overcooked, and the soup had a significant amount of chicken that clearly came from a whole bird, not a denatured breast, and it was actually spicy, too.

My favorite thing to order at a diner is an open-faced hot turkey sandwich (the ultimate tribute to Thanksgiving), and the open-faced hot turkey sandwich at the Square Knot Diner in Georgetown is outstanding. There are hunks of both dark and white meat, some of it crisped on the edges; the gravy is not too thin, not too thick, made in-house with the right amount of salt (and they may offer you more, unbidden); the potatoes are creamy, with a faint, mysterious, wonderful lemony flavor. The portion: gigantic.

Here is a thing you should never order at a diner: a Caesar salad. (At a nouvelle, upscale diner, sure; Skillet makes one—with kale. It is good, but should a place serving a kale Caesar be allowed to use the word "diner"?) I tried the Caesar at the Square Knot to re-test this truism, and lo and behold, it was made with indifferent lettuce, glops of dressing, industrial-gauge Parmesan, and house-made but not fresh-tasting croutons.

A diner's breakfasts are arguably its true test. At the Square Knot: crispy-browned on the outside, tender on the inside, shredded hash browns. Thick-cut, tasty bacon. Not-too-heavy pancakes. And the eggs Benedict is great: especially hammy (but not overly smoked) ham and a hollandaise that's creamy but light, whispering of lemon, not shouting about it.

The only real hitch is the pie. The slice of apple pie I had at the Square Knot was barely passable; the filling was fine, made with tart apples and properly cinnamony, and there was plenty of it, but the crust was pale and doughy, chewing to a paste instead of flaking apart all butterily in the mouth. Instead, you should get the 9 Lb. porter milkshake, a vanilla shake with chocolate syrup and porter beer; the porter forms little icy porter-pockets, like the ones you get with a root beer float, and it nudges the whole thing away from sweet. It is an excellent innovation: approved.

The Square Knot opened in May and has not closed since. It is there for you, 24 hours a day, the way a diner should be.