The show has been sold out, every ticket, for every day of its four-month run, since before it even opened its doors. That is a phenomenon more commonly associated with U2 concert tours or limited-run Broadway musicals, not stately, informative expositions of old pictures. But London's National Gallery has a show on now that lives up to the hype, one which is well worth trying to sneak in to see. Next thing you know, there will be ticket-touts in three-piece suits outside the gallery doors, scalping tickets for ten times the asking price to desperate fans. And I wouldn't blame them, because this is one heck of a show.

"Leonardo: Painter at the Court of Milan" (November 9-February 5) is the largest exhibition of the work of Leonardo da Vinci ever displayed. Before this exhibit, Leonardo had only eighteen universally agreed upon portable paintings attributed to him. A newly discovered Leonardo, once part of King Charles I's art collection but then lost, also appears in this show, bringing the total to nineteen worldwide. Nine of them feature here.

Most art museum shows come in one of three varieties. There is the survey, in which works are gathered together so that they may be admired and studied in one place. These surveys might cover a style (Mannerism in Ferrara), an artist (El Greco), a period and place (1920s Paris), or a chapter in an artist's career (Picasso's Blue Period). Another category is the star-turn, a first chance to display a famous work in a new location. The best-known instance was the tour of Leonardo's Mona Lisa (understandably not included in this London exhibit, otherwise there would have been stampedes and riots to get in), which was displayed in Italy after it was recovered from the thief Vincenzo Peruggia, and visited Japan and the United States in the 1960s and '70s. Finally there are exhibits that are primarily informative rather than crowd-pleasing, the sort that expect you to read all of the wall copy, and perhaps the catalogue, shows that you slowly imbibe rather than rush through. Shows with titles like "Tile-Making in 17th century Delft" may be lovely and are certainly educational, but they have a rather more limited popular appeal, and are in no danger of selling out prior to opening. Most museum shows fit the third category, fulfilling the role of museum as preserver and educator, not primarily as entertainer. But "Leonardo: Painter at the Court of Milan" embodies all three in one gorgeous package—and the catalogue that accompanies it is both gorgeous and richly informative.

This show gathers all of the extant paintings that Leonardo worked on during his tenure at the Sforza court in Milan (1482-1499). The only exception is the immobile and precariously preserved Last Supper, a wall painting represented here by a very good full-scale copy in oil on canvas by Giampietrino. This copy, made circa 1520, is actually far easier to see than the original, which has lost so much of its detail. In addition to the nine Leonardo paintings, assorted drawings and pictures from his circle bring the total works on display to a meaty ninety-three.

The resulting show is educational, if one can hack one's way through the throng of white-haired, well-dressed museumgoers and get close enough to read the wall copy and admire the details of the small drawings that flesh out the exhibit. When I went, I was the only person I could see who was under the age of fifty. But since I was significantly taller than most of my fellow visitors, I had a good advantage. Such crowded exhibits, full of waiting and arm-jostling, exact their toll, but when something this good comes along, an exhibit that may indeed be once-in-a-lifetime, it's worth fighting for.

Without doubt the highlights of this show are the Leonardo paintings, to such an extent that the drawings and paintings by others in Leonardo's circle, such as Boltraffio (who seems to have been completely fascinated by puffy-lipped youths with a slight overbite), feel like filler. That's a shame, because every piece in this show is of interest. I had no appreciation for Boltraffio before it, and now I do (despite the lips, or perhaps because of them). But the tidal wave of visitors thunders from one show-stopper to the next, and there are plenty of them to be found.

If there's one reason above all others to see this show, it's the chance to admire "Lady with an Ermine (Portrait of Cecilia Gallerani" (1489-90), which is normally housed in Cracow—not on everyone's traffic pattern. This picture is every bit as nuanced and wonderful as "Mona Lisa," and I would have been content staring at it alone for a good hour. The sense of welcome, anticipation, and excitement is heightened by knowing just how hard it would be to ever see this work again. Were it in Paris or Rome or Madrid one might be able to convince oneself that there would be other times when it might cross one's path. But people fly to Cracow specifically to see this work, and having seen it in person for the first time here, I can say that it is worth the journey.

Beside "Lady with an Ermine" hangs "La Belle Ferroniere (Portrait of Beatrice d'Este)" (1493-94), one of many works here normally in the Louvre collection. This is not to be confused with the so-called "American Leonardo," a copy of "La Belle Ferroniere" that just might also be by Leonardo and which was the subject of a famous court trial in which Bernard Berenson and Joseph Duveen testified. The Louvre painting, certainly an original, is brooding and has a melancholy to it that stands in sharp contrast to "Lady with an Ermine," in which Cecilia Gallerani has mischief in her quarter-smile as she lovingly strokes the ermine. The curators have set up a wonderful duel between "La Belle Ferroniere," wife of Ludovica Sforza, and "Lady with an Ermine," portrait of Sforza's beloved mistress. The former seems to stare in quiet rage at the portrait of the latter beside her. We can see why Sforza might have favored Cecilia.

The next tremendous coup for this exhibit is the juxtaposition of both versions of "Virgin of the Rocks" in the same room, one from the Louvre and one from the National Gallery. The Louvre version, from 1483, features captivating geology, rocks like canines, stark against the lovingly-rendered Madonna with John the Baptist and an infant Christ. Across the room, which is spiked with preparatory drawings that give a glimpse of Leonardo's process, hangs the National Gallery version, from 1492-99: ghostlike, the figures pale and mannered, shadowy and twilit. Though the composition is similar, the handling of the human forms might as well have been by different painters. Simply turning one's head from one version to the other is a great treat (it made me want to send the curators a fruit basket in appreciation).

Such is the hype surrounding "Lady with an Ermine," the two "Virgins of the Rocks," and the newly discovered "Salvator Mundi" (of which more in a moment), one might easily forget some smaller treasures that are in the mix. The unfinished and quite awkward "Penitent Saint Jerome" (1488-90) is here from Rome, complemented by drawings, as well as the odd "Madonna Litta" (1491-95), a reworking of the traditional lactating Madonnas. If you sneeze you might walk past the tiny "Madonna of the Yarnwinder," which was thought lost for good—it had been stolen in 2004 from a castle in Scotland and was only recently recovered, found in the offices of a Glasgow law firm that had been holding it for the gangsters.

Much of the drum-roll about this exhibition was the inclusion of a never-before-seen lost Leonardo painting, "Salvator Mundi" (circa 1499). Now owned by a consortium of collectors, the work had featured in the royal collection of King Charles I, but had been damaged and its attribution lost until recently. The current owners assured the National Gallery that they had no imminent plans to sell the work, a rule of the gallery to ensure that their display of a work is not tantamount to advertising. A similar assurance could not be made for another lost work that some scholars think is by Leonardo (although many fewer than the near-universal agreement about "Salvator Mundi"), called "La Bella Principessa." Hence it is not included in the exhibit. Either one of these two "lost" works, both of which are in private hands, could break the world auction record for an Old Master if sold: Rubens' "Massacre of the Innocents" fetched only 49.5 million pounds, about a third the price of the top Modern painters.

The moment you stand before "Salvator Mundi" there can be no doubt that it is by Leonardo. Its handling is masterful, its detail striking and very much in keeping with the style of the master throughout the show. The reddened eyes of Christ as savior of the world, as if he has just wept. The rock crystal orb in his hand, representing not just the world but the universe. The puffed and rubicund lips (which perhaps inspired Boltraffio's love of bee-stung overbites), the delicate sfumato used to mask the figure in a smoky haze that only emphasizes the mysticism of the work.

Wandering through this exhibit makes one feel blessed, thankful to the good folks at the National Gallery for bringing together so many wonderful pictures that inform and enchant. With so much to see in the pictures, one hardly has time for the wall copy, and the stifling crowds disappear as you stare with awe and a great sense of peace, at some of the world's greatest paintings, by one of the world's greatest painters.

Noah Charney is professor of art history at American University of Rome. He writes regularly for ArtInfo and Tendencias del Mercado. His latest book is The Thefts of the Mona Lisa: On Stealing the World's Most Famous Painting (ARCA).

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