Gliding between the tables of fashion models and millionaires, kissing hands and patting shoulders, the barman pauses at a photo above my chair.
"I would say that was taken at La Poulard at about 12 o'clock on 25 August 1944," he muses above the chatter. "Robert Capa on the right has just taken the famous photos on the Normandy beaches, and Hemingway at the end of the table is about to liberate Paris with seven men. Or as he put it – liberate the cellars of the Ritz."
He slips a glass of mist-coloured liquid on to the table in front of me. "You're sitting in the chair where Hemingway's son Jack used to sit in later years. Try this cocktail. It's one of mine. We call it Serendipity."
The cellars of the Ritz, and especially the Hemingway Bar at the Ritz, seem a good place to start my exploration of Paris in the Twenties. They seem even better after a sip of Colin Field's exquisite mix of calvados, champagne and mint. No wonder he's been voted the world's best barman, twice. And a glance around his wood-walled bar, its panels crammed with prints of Hemingway, its tables crowded with beautiful people for Paris Fashion Week, is enough to seal the deal.
I'm here to find places where you can still catch an echo of that era, the glittering years between the wars when Paris shook up a cocktail of its own – from art, jazz, fashion and money – whose flavour is with us still. My prompt is an exhibition opening this week, of the legendary but long-lost collection of Modernist art once owned by resident American, the experimental writer Gertrude Stein.
In this city, she redirected the flow of modern fiction, while Coco Chanel shaped modern fashion. Scott Fitzgerald trumpeted the jazz age in his stories, Picasso exploded painting into Cubism and Dali lulled it into dreams. "Paris," said Stein, "was the 20th century. It was the place to be."
Right now, the Ritz seems to be the place to be, as the clock touches 2am and I drift towards my bedroom. The corridors are impossibly grand. Somewhere upstairs I find the room, its cream walls scrolled rococo-style, its bathroom a fantasy of marble and gold. Beside the bed, gold buttons allow you to summon a waiter, housemaid or valet.
But I'm searching for something else, so next day I leave the glamour of the Right Bank and walk on to the Left. Here, near the spires of Notre- Dame, is the city's other shrine to the Twenties. A rackety bookshop, its low-beamed ceilings lit by dusty candelabras, its maze of rooms packed with red-leather tomes beside the bright bestsellers of today. A poster proclaims: "Be not inhospitable to strangers, lest they be angels in disguise."
This is Shakespeare and Company. For 60 years it has welcomed strangers, as customers or as guests. Hidden among its book-stacks, disguised as sofas, are pull-out beds where penniless writers can stay for free, in return for help in the shop. More than 50,000 hopefuls have stayed at this "Tumbleweed Hotel". As I will tonight.
The shop's name and ideals are reincarnations of a famous bookshop of the Twenties, run by the American Sylvia Beach. It became an informal club for experimental and usually impoverished writers, with Hemingway as its favourite friend and James Joyce as its patriarch. Beach bravely published Joyce's Ulysses in 1922, defying public scandal. It made her reputation.
Today's bookshop is run by Sylvia Whitman, who was named after the first Sylvia. "It's a dream to work here," she says, "surrounded by a circus of books and eccentric people constantly in movement. I think Paris still holds a very literary weight for aspiring writers. The literary history is rich here, the river is lined with booksellers, the city is made for walking, the cafés are for long hours of thinking and taking notes. Maybe I'm a romantic, but I still envision Paris in that way."
Among the books on the first floor is my bed for the night. At 11pm the shutters go up on the shop, the Tumbleweeds conjure their bags from hidden cupboards. My bed has a crumpled red duvet and I fall asleep beneath hardbacks with such names as Memoir of Scott Fitzgerald, Being Geniuses Together and Gertrude Stein Remembered.
Next morning I awake to the bells of Notre-Dame. I slip out and catch a Métro to the Closerie des Lilas, a lovely old café frequented by writers for ever. Here we are close to how it was. The old bar is a dim-lit Art Deco room, with brass nameplates recording the names of past customers at the tables. I sit at the place of Edvard Munch. Nearby are Jean-Paul Sartre, Man Ray, August Strindberg and Lenin. On the counter, next to the ice bucket, is Hemingway.
Surfacing, I head for the Lutetia, the city's finest Art Deco hotel. This is where Picasso spent his honeymoon after marrying a beautiful dancer from the Ballets Russes in 1918. The façade is a sinuous ripple of masonry, curving like a Gaudi. The interior is period perfection. The bar is lit by two huge bronze statues of women clutching bulbs of light. The brasserie is a blaze of chrome and mirrors, where customers in curving banquettes eat shellfish on ice. There are fashionistas in the bar, and jazz till 1am, and a hedonistic spa. Of all the places I've
seen so far, this one is the time machine. But I'm off to the Rue de Fleurus. Here, from the 1910s, Gertrude Stein held Saturday salons. And it is Stein who has drawn me to Paris. On her walls she displayed an astonishing collection of paintings by daring unknowns including Picasso and Matisse, paintings that she was the first to buy. She was a patron to young writers, too. Visitors came to view the avant-garde art and talk to the author – who said she had invented the styles of Joyce, Proust and Hemingway.
After her death, the collection dispersed. But this week it has been reassembled at the Grand Palais. It's a once-only opportunity to step into that time. Her studio is in a courtyard barred by glass doors. I lurk. Someone comes out. I flit in. Down a path is a square of bushes, and then on the right the famous apartment. Nothing special, a flat front painted cream. Lights turned out. But this is where they walked, all those pioneers.
To meet a living pioneer, I travel to the rougher quarter of Ménilmontant. Here lives a 94-year-old painter who just caught the inter-war years. Alfred Rozelaar Green came here in 1938 as an art student from London, and stayed for most of his life. We sit in his garden beneath a vine with his wife Betty, eating omelettes and strawberries. They laugh at old memories. They tell me how they met, putting on an avant-garde play called Yes Is for a Very Young Man – by Gertrude Stein. But this was 1948, just after her death, and they never met her.
Alfred recalls the pre-war artist's life: days spent sketching from 9am till 10pm, nights at the Bal Nègre dance hall, where Afro-Cuban jazz was the rage. From 6pm, the place to meet was the Dôme café, two streets from his digs, a favoured haunt of bohemians to this day. And one night he took home with him the woman who became his first wife: Nita, who had been a model for Matisse.
They remember, too, hanging out with Picasso on the beaches of the Riviera. "So playful he was," smiles Betty, "always fooling about. In those days you could go into a café and see someone famous and just talk to them. Not like England!"
And they remember me, as a little boy, born in Paris in the cold winter of 1963, when my parents had run away from London to be artists together. My parents used to speak of meeting Picasso and Dali and Sartre, and an aged concierge who once was Rodin's model. But they had not known the older Paris. And I have not visited Betty and Alfred for 30 years. We are all travelling in time.
Finally, I say goodbye and head off to the Stein show. It is superb. There is a wall of early Matisses in their wild colourings, shimmering Cézannes, and precise Cubist works by Picasso and Juan Gris. There is Picasso's masterly portrait of Stein herself, a grumpy woman in brown. She complained that it did not look like her, and he warned her that in the future it would.
And then there is Picasso's self-portrait in his twenties. Not the bullish conqueror with the burning eyes of later years, but an awkward, unsure younger man – a penniless arrival in Paris, wondering how to make his mark. I look into his eyes and see fear.
And I finally grasp that this is what Paris gave them all, and why it happened here. This raffish city offered sanctuary, and the promise of a dream that for some of them came true. It's why travellers come here still.
That dream of Paris was captured best by Hemingway. His youthful breakthrough, the novel that took him from hunger to the Ritz, was The Sun Also Rises in 1926 – a hymn to bohemian life in Paris. And his final book, worked on till his death, was A Moveable Feast, an old man's attempt to recapture that time – "the early days when we were very poor and very happy". It's as close as you'll ever get to being there.
He started writing it in 1957, after being given two suitcases full of notes from the period. They had been stored all those years in the cellars at the Ritz.
How to get there
Jonathan Lorie travelled as a guest of Atout France, the France Tourism Development Agency (09068 244 123; uk.franceguide.com) and Eurostar (08432 186 186; eurostar.com), which offers return fares from £69 from London St Pancras International. He was a guest of Ritz Paris (00 33 1 43 16 30 30; ritzparis.com), which offers rooms from £730 per night, and Hotel Lutetia (00 33 1 49 54 46 46; concorde-hotels.com/lutetia), which offers rooms from £190 per night.
Matisse, Cézanne, Picasso...L'Aventure des Stein is on at the Grand Palais, Paris, until 16 January (00 33 1 40 13 48 00; rmn.fr ). Shakespeare and Company (00 33 1 43 25 40 93; (shakespeareandcompany.com).