11 p.m. The night begins at Bernard's office party; one of scores of office parties going on in Dublin this second Friday before Christmas.

Architects sure throw a classy party. In Murray O Laoire's converted warehouse in the Liberties I'm dancing to a live salsa band and hoping I'm not going to blow all my energy for the evening in the process. There are films projected on the walls, swirly colours from oil lamps on the ceiling, lots of gyrating hips and perfect cha-cha-chas. Since my own knight currently lives in Edinburgh I've borrowed one for the night, Bernard Gilna. Everyone is having a wild time, there's a free bar, amazing caterers, great music.

1.15 a.m.And there we are, gone, leaving it all behind us. "Where are you going?" a colleague hollers in amazement at Bernard as we head for the door. " On a mission," he says.

1.30 a.m.South Great George's Street is thronged. Girls in thigh-high boots linking arms and wearing tinsel round their necks. Someone is singing a drunken Jingle Bells. Bernard inspects the pavements with a professional eye. "It isn't a night out until you see lots of vomit." He doesn't have to search for long.

There's a big shuffling queue in the Dame Street Spar: people are buying litre bottles of Coke, sweeties by the armful, and clearing the shelves of the last egg sandwiches. It's a widespread attack of the munchies. Opposite Trinity we count over 80 people waiting for a taxi.

Since December 4th Dublin Bus has been running Nitelink buses every night bar Sunday, serving 14 routes throughout Dublin. They depart from the city centre at midnight, 1, 2 and 3 a.m., to Blakestown and Blanchardstown, Sutton and Stillorgan and scores of other destinations. In Dublin argot they are referred to as the Vomit Comets. The service will continue until January 3rd.

2 a.m.We board the 46A Nitelink to Dun Laoghaire. The bus is about a third full and we sit upstairs, in the middle. In front of us are five people sitting alone and one couple, asleep on each other's shoulders. The woman has a single yellow rose on her lap. The man stirs and strokes her hair.

Sitting at the back are a group of lads. Night or day, lads always seem to sit at the back of the bus. Snippets of their conversation carry down to us: "What are these f**** telly-bellies that everyone's farting on about?" "The police brought him into the station. . . I'm telling you they did."

Then suddenly, big panic. They think they're on the wrong bus and start clucking like agitated hens, looking out the window for landmarks. "Where are we going?" "To Dun Laoghaire." "Are ya sure?" "I think so." "Yeah, but are you sure, are ya?"

We pass RTE, where the pylon is lit up like a rocket. Beyond Stillorgan someone is kicking a road sign that says Proceed With Caution.

2.25 a.m.We're outside Dun Laoghaire DART station waiting for a taxi. There are men working on the roof of the new station, the lights on their helmets like stars. The last stragglers from an office party are coming out of Brasserie na Mara.

"Where are we going now?" a woman calls, holding a bunch of about 20 pink and purple balloons. She tries to bring them into the taxi with her. Everyone except the taxi driver is howling with laughter.

3 a.m.Dunnes Stores, Cornelscourt. For the Fridays of December, Dunnes keeps its flagship store open 24 hours a day. It's the American concept of shopping. I look around the car park. It's pretty empty. And it's cold: a clear night. Shivering, we go inside, fully awake again, on our second wind.

What I really want is a shot of whiskey, but have to settle for an All-Night Breakfast in the Timepiece Restaurant overlooking endless rails of clothes.

Who willingly goes shopping at this hour of the morning? I leave Bernard tucking into rashers and sausages and talk to a party of five from Gorey at the opposite table. They all work together in Brennans Pub and have driven up in the one car after closing time earlier that night.

"It's the novelty," Nuala Kinsella explains. What have they been buying?

"Tea towels," says chef Catherine Kavanagh. She's not joking. She was also looking for aprons but couldn't find the sort she wanted.

"It would have been a lot more fun if the off-licence was open," reports disgruntled barman Noel O`Brien, pointing out correctly that booze-buying forms a central part of many people's Christmas shopping. He settled for buying a pair of shoes instead. Barmaid Corrina Doherty has bought a bra. They're just about to head for home .

There are voice-overs on the tannoy, advertising the late-night opening hours. The girl behind the counter says they're very quiet, same as it was last week. Someone drops their All-Night Breakfast with an almighty crash. Circles of black pudding roll by on the floor.

Four women and a young girl are at another table. They're from Celbridge. They say it was busy earlier on, around midnight, when a consignment of Teletubbies went on sale.

"You can go round in peace at this hour," Rose Kearney says, when asked why they're here.

"We've been shopping for presents. Mostly clothes," Patricia Kearney, Anne Hughes and Olivia McGuire chorus.

"We had great comfort parking the car," Olivia adds. Her daughter, Cheryl, bought a Matilda video and a lunchbox. "It's so relaxing here," Cheryl says. She's 13.

3.45 a.m. Outside the Timepiece, we meet novelist Colm Toib in and architect Denis Looby. They've been to the Hospice Ball out at Powerscourt in Enniskerry and are in full evening dress and look bizarrely out of place among the rails of fleece jackets and micro minis. Colm has bought a pineapple. "A fine specimen," he pronounces, pulling it out of the bag and holding it up for us to admire. We all start giggling. The ads for all-night opening come on the tannoy again and we fall about. By then the only people in the restaurant are the staff.

4 a.m. I take a trolley and start pushing it up and down the empty aisles of the supermarket. This is when the night becomes ever more surreal. Finding the artificial light of supermarkets sophorific at any time, I now begin to feel as if I'm in a dream - or is it a film set? It's one thing to stay out all night, quaffing in some tasteful dive, but I've never been out this late with the sole purpose of shopping for washing-up liquid and bun cases. Apart from a veritable army of staff stacking shelves there are only two other customers in the entire supermarket. Neither of them wants to be named. The man's basket is full of bleach, detergent, rubber gloves, black bin-liners and something that looks like a box of Attack-a-Rat. There are deep hollows under his eyes and. "What I love about 24-hour shopping is that there's no closing time," the woman says with glazed eyes. "I can just keep on shopping and shopping." Her trolley is crammed with catfood and ready-made meals for one.

4.30 a.m. We load my household shopping into the boot of the taxi. It takes only 10 minutes to drive from Cornelscourt to central Dublin where we drop the bags off at the house. Since we have become unwillingly used to the traffic which seems to permanently clog the roads, this 10minute journey is now a revelation. Psychologically Dublin seems enormous when it takes so long to cross the city, and yet, the geographical distances are not that great. Dublin, I discover in these graveyard hours, is really a small place.

4.45 a.m.The allnight cafe on Camden Street, the Billboard. It's full and it's buzzing. The Beatles are blaring and we have to shout to be heard. "We do a great All-Night Breakfast," the waitress tells us brightly. Bernard groans. We order cappuccinos.

Carol Lakes is sitting across the way. She was working late in a pub and waited two hours for a taxi before giving up and calling her boyfriend to rescue her. They're having something to eat before heading home. How many people were waiting for taxis? "Hundreds," she says grimly. "It's just lucky it wasn't raining."

Sisters Eimear and Amy McMahon are tucking into garlic fries and cheesy toast. They've been clubbing in Buck Whaleys on Leeson Street. "It was mad," Eimear says. "All the office parties were out. We had to queue for half and hour to get in, for the first time ever. But it was brilliant, once we got in." Sassy, bright-eyed and beautifully dressed, the sisters are effortlessly fending off the attentions of the less composed men at nearby tables.

We've now been joined by Brendan. He has seen my notebook and wants to know what's going on.

5.15 a.m. Time for a shaggy dog story. Brendan obliges spectacularly. He says he has a story which he's thinking of telling on The Gerry Ryan Show. "I could destroy careers in this city," he says. "I know things that would bring people down. But I'd ruin my own job if I did it. We're talking big corruption here. Very big." Brendan never does tell us the story he might one day tell Gerry Ryan and the nation, but he does ask me not to use his surname. "I skipped work for the day to go Christmas shopping and ended up in Break for the Border," he admits sheepishly.

5.45 a.m. We start walking towards town. It's dark and silent and cold. The pavement strikes up chill under my feet. The silence is very peculiar and a bit unnerving. An insomniac bird twitters in St Stephen's Green. A sea of rubbish is silted up against every doorway; squashed beer cans, chip papers, burger boxes. At Dame Street the corporation lorries are out washing down the pavements and collecting rubbish. Outside the Bank of Ireland on College Green, men are unloading newspapers. Approaching the GPO, a man is posting handfuls of white envelopes. "Christmas cards," Bernard suggests. "Must have been writing them all night."

6.15 a.m. Henry Street and Mary Street are shuttered and empty. Dimly-lit side-streets run off them like dark tributaries. My feet are freezing. It now feels later and darker than it did at three in the morning: as if the night will never end. "I'm tired," someone says and I realise the voice is mine. Coming up to Smithfield the fruit markets are opening up. We pass the Fyffe Banana warehouse. It's like a science-fiction movie. Juggernauts and motorised forklifts hiss past us in the darkness, moving crates from lorries to warehouses.

6.35 a.m. Smithfield market. It's piled high with Christmas trees. The air is sharp with the smell of pine-needles. Thousands of trees have just been unloaded from the back of vans and lorries and each bay of trees has a couple of silent guardians who watch us with mistrust. Who in their right mind would come sightseeing around here at this time?

6.50 a.m. Doubling back along the quays. I am keen to have an early-morning pint in Slatterys of Capel Street which opens at about 7 a.m. to cater for the people working at the markets. We've passed it a bit earlier and it was still closed. We are killing time now. I ask Bernard how he's feeling. He points to the derelict building on the quays that we've just passed. "Like that," he says. "Vacant." We abandon plans for an early morning pint. Pity.

7.10 a.m. Parliament Street. Bernard goes in home. I hail a taxi. Collapse into squashy seat. Somewhere along the way I must have left my brains behind me. Forget to take my brand-new black suede gloves out of taxi.

7.30 a.m. Rail at loss of gloves. Fall into bed.