''Look! Look! It says Dodi!" The fat lady jabs excitedly at the glass case; her companion - thin, dingy, perhaps her daughter - squints at the paper within. It is the typed draft of Earl Spencer's address for his sister's funeral, and, sure enough, it contains a sentence - crossed out in pen - thanking Dodi "al-Fayed" by name for helping to make Diana's last weeks happy.
"You see," says the lady, "so he was the one."
It's a damp Wednesday morning, and although the crowds at Althorp are thin for the first week of the visiting season, a fair number of them are squeezed into the stables for the exhibition entitled "Diana: a celebration". In this particular room, there are about 20 people. Most look over 50. Most have that "smart casual" look that one associates with the British middle classes at leisure. All are female - apart from me, and a morose younger man with cropped hair, tracksuit bottoms and both hands clenched in alarmingly large fists.
Despite the piped music, they talk in hushed voices, as if from reverence for the relics around them. This results in a number of irritated "What?"s. But the mood is otherwise calm. Rather than jostle around the best exhibits, the visitors work their way round the room in a queue, patient as supermarket shoppers.
They linger longest at the wedding dress. "Oh, it's beautiful, isn't it?" "I thought it would be more, like, puffed out." "They keep it at the exact, you know, temperature." "We missed it, you see. We were in Wales. But we were able to see it on the television."
In the next room, an audiovisual display tells us about Diana's good works. It is almost empty. The room after that has a similar display, but more compelling. A flickering screen shows images of those extraordinary days, five years ago this summer, when this posthumous cult was born: a sea of cellophane and flowers glinting in the sun at Kensington Gardens; votive offerings stuck to railings; hordes of wild-eyed mourners roaming streets that echoed with the lamentations of a hitherto voiceless "people".
In the months that followed, there was much talk of a new, softer Britain; and, in this part of Northamptonshire, of an economic windfall. Althorp, made over, became (arguably) Britain's busiest stately home (with 2,000 visitors a day during last year's visiting season). For local hoteliers, caterers, souvenir-makers, florists, guides and many more, the opportunities for cashing in seemed limitless. My local pub, roughly 20 miles to the west of Althorp, reinvented itself as "England's Rose", a kitsch shrine for passing coach parties, packed with chintz sofas, photographs of the late princess and a framed letter from Mohamed Al Fayed.
Five years on, the hysteria has ebbed. William and Harry (along with Posh, Becks and the stars of reality TV) are superseding their mother as media brands; Diana's royal enemies have been largely rehabilitated; to denounce Diana as a manipulative snob is no longer to risk public lynching. It's a long time since I saw a coach outside England's Rose, or, for that matter, a really shameless piece of Dianography in the media.
But now it's anniversary time. Newspapers have the scent of their favourite quarry in their nostrils again (witness the fountain controversy, and the Guardian's respectful interview with Earl Spencer earlier this month). And Althorp, similarly, is expecting a revival. More than 1,000 advance coach bookings have already been taken for this summer, and the house is extending its opening period by a month (no longer July to August, now July to September) to deal with the anticipated extra demand.
This may or may not materialise. Althorp did well last year, despite foot-and-mouth; but the previous three years saw a marked downward trend in visitors and, more noticeably, in profits donated to charity. It is hard to imagine visitors from overseas being as keen as they were before 11 September, and as for native Dianaphiles - well, they can't still be in the state they were in five years ago. Or can they?
The visitors I ask offer a range of explanations for their presence there: "I just thought it would be interesting"; "I'd never been before"; "I was always fond of Diana and I wanted to see where she grew up." Some seem uncomfortable about articulating the emotions that have brought them here; for others, emotions don't come into it - they are stately-home visitors rather than Diana junkies. If any are motivated by mawkishness, they conceal it better than those wailing mourners did five years ago.
Around the house, which is packed to the point of ostentation with Old Masters and other treasures, the off-guard murmurings are predominantly phlegmatic in tone: "Must be worth millions"; "Imagine cleaning that lot"; and so on.
Outside, at Diana's shrine, the mood is harder to gauge. She is buried on an island in a lake to the north-east of the house. Getting on for 100 bouquets have been left around the mock- classical "temple" (complete with Diana silhouette and inscriptions) at the far end of the lake. This may, however, have something to do with an imaginative marketing offer at the nearby Fox & Hounds, where you can get a free bouquet with each purchase of morning coffee.
The visitors - mourners? - circumnavigate the lake with characteristic patience, all at the same solemn pace and all (for no obvious reason) in the same clockwise direction. But they are not noticeably subdued. "Charles never went to Eton," a grand battleship of a lady explains to her companion. "He went to a tough school in Scotland, the same one as his father. I think he was happy there." A frail-looking man with a leathery suntan is carrying a miniature television on which, to the irritation of his female companions, he appears to be watching Wimbledon.
A young American woman loudly quizzes an attendant about the origins of the island: "Did they, like, dig round the island? Or did they build the lake first and then put the island in after?"
On the other side of the house, an elderly couple are inspecting an avenue of young oaks which, according to a nearby plaque, was planted by Earl Spencer to commemorate his sister's life.
"He must have thought the world of his sister," says the woman, "to do all these commemorative things for her."
"I'll tell you what," says the man, "he thinks more of her now she's dead than he did when she was alive."
The woman considers this. "Given him an income, hasn't she?"
"Best thing's ever happened to him."
Such cynicism would no doubt appal Earl Spencer, who would point out that all the profits from the enterprise go to the Diana, Princess of Wales Memorial Fund. Yes, the products in the gift shop ("selected by Earl Spencer and designed exclusively for Althorp") may seem exploitative - cynical, even, in the light of Earl Spencer's recent claim that he wanted "to put a line under being the man who made the speech at his sister's funeral". (Bargains include: Special Edition Collector's Enamel Box, with quotation from Earl Spencer's funeral address inside lid, £50; Earl Spencer's Tribute Book, a silk-bound volume of that same funeral address, £20; Commemorative Fine Bone China Plate, including silhouette of Diana and the motto - quoting from the address - "compassion, duty, style, beauty", £75 . . .) But it's all in a good cause; and if £615,251 doesn't seem a huge amount to have generated for charity from the first 390,000 visitors (1998-2000, excluding the 1998 benefit concert), it's better than nothing.
In any case, Althorp isn't just about money. It's also about remembering someone who, whatever her faults, performed more kindnesses to more people than most of us will get round to meeting in lifetimes twice as long. For many people, that function needs no financial justification.
And why should it? Even the most sceptical reading of "Diana: a celebration" cannot disguise that her story was, among other things, an ordinary human tragedy of dashed hopes and inexorable mortality. The exhibition makes the most of this, and - annoyingly - it often works. Whatever your cynical prejudices, you would need a heart of stone to look at the childhood letters and family photos without feeling some sneaking sense of pathos. And most visitors to Althorp are not overburdened with cynical prejudices.
On the way out of the exhibition, you are confronted with an entire wall of condolence books: hundreds of them, from all over the world, from great biblical leather ones, sent by governments, to flimsy pamphlets from their humblest subjects. The sheer range is breathtaking - humbling, even. Is this final evidence that, five years ago, the whole world went mad? Or does it, rather, commemorate a moment when the world (intelligentsia apart) remembered its heart, and briefly became a better place?
As the patient visitors work their way down the great glass case that contains all the books, the man with the fists points to one of the humblest: an exercise book from Class 2, Parkend Primary School in Lydney, Gloucestershire. "Look," he tells his female companion. "Look at that!"
He cannot continue. The emotion leaves him choked. From beyond the grave, the Queen of Hearts triumphs still.