The small man studies his hostess, weathered face creased in amusement, and wonders how it is that certain women can drip with jewels without losing their plausibility. He shambles over to the bar, holding up his glass for a refill: Irish on the rocks. With a nod to the scruffy bartender, he straightens the lapels of the rumpled Panama suit he has donned in deference to the occasion, and turns to study the elegant company - two handsome young men and three poised, well-dressed women. He smiles as he holds up his glass in salute.

'I never could get the hang of champagne,' he says. 'Don't get me wrong - I like wine, and I love fizzy water. Just not in the one glass.' He grins puckishly. 'My most memorable night in the tropics? You shall have it - with adventure and a bit of naughtiness, I promise. Sophistication? That is harder, but I think I can add a touch to the story - if you'll admit intellectual sophistication, which is the only kind I can manage. As I am the Peter Lorre of the group - funny accent, there for the comic relief - I think I should go first.

'Basically, I hate the tropics - I was born in the subtropics, and that is quite enough heat and humidity for me. Enough bugs, too. I prefer the Mediterranean, which is where my story begins. Back in the eighties, I was teaching English in Athens. I happened to buy a handmade shirt in one of those stalls in the Plaka - you know, the stripey kind they sell to tourists. They were cheap and comfortable, and as you can tell, sartorial elegance is not in my repertoire. When I took the shirt home I found a real treasure in the pocket - a little faded by being put through the laundry, but still a genuine find.

'I say a treasure, but what it was, was a treasure map. As I studied it, I grew terribly excited - the map, which was of the coast of Madagascar, showed where to find the wreckage of the Donegal Queane, the flagship of the notorious 18th-Century Irish buccaneer Brendan O'Rahaileagh, who met his death there in a desperate pitched battle against half a hundred Malagasy pirates. I am somewhat of a student of pirate history, and I was determined to go find the ship.

'I enlisted the help of my two closest friends, Hector Hunt from Sheffield, like me an English teacher in a local frontistirio, and Philautos Papamichaelidis, son of a Greek shipping magnate. Phil opined that he could get a yacht from his dad, easy, no problem, then pirazi, it was a better idea than that bilingual punk-folk band we had started, so as soon as the semester was over, the three of us set off to Madagascar in the Melina Mercouri, long nights under the stars and long days of fruitless searching - and constant bickering.

'Phil took advantage of every port stop to woo the local maidens, while Hector whinged endlessly about everything - the food, the natives' insistence on speaking Frog, his inability to acquire that sine qua non of English civilisation, a copy of The Times, the fact that our short-wave wasn't picking up the BBC reliably...we'd seen no sign of a sunken ship, just lots of cheeky monkeys and one unconfirmed sighting of John Cleese.

'On the tropical night in question - the air heavy and damp, like breathing wet cotton - we were all on edge. The captain was puttering us about the starlit lagoon in hopes of catching a vagrant breeze. Hector, his ire fueled by flat beer, was hectoring Phil about his amours, while Phil was shrugging over his favorite tipple - a vintage Tokay - and then pirazi-ing in high Greek style. I leaned against the railing, so disgusted with the both of them that I was drinking Metaxa - two-star, no less - straight out of the bottle. Then it happened. The boat took a sudden turn to avoid a snag, and I fell overboard.

'In the spill, I lost my Metaxa and my spectacles, but not, I fancied, my poise. Coming up for air, I glimpsed the yacht in retreat and realised I wouldn't be able to shout above the noise of the engines and their arguing. So I decided to swim for shore - the water was calm, and I am a strong though awkward swimmer.

'As I breast-stroked along, I began to worry about two things: the shore was farther away than I had thought, and I couldn't remember if there were sharks or crocodiles in these waters. I didn't mind drowning - I've almost done it a few times - but I have a visceral objection to being eaten.

'Then something pulled me by the right ankle, and under I went.

'The something wasn't sharp enough for teeth, though - rather gentle, but firm - and when I opened my eyes I saw a sight far more welcome than Bruce the Great White. The most beautiful woman I had ever seen - well, half-woman, the other half fish, if you want the truth - had let go my ankle and was seizing my arm. Her long, red hair swirled around her face, and her green eyes glowed as she pulled me further down into the lagoon, down to the waiting...ship...below...

'It was the Donegal Queane, in her final resting place at the bottom of the lagoon - now less an 18th-Century sloop than a habitat for marine life, its masts and hull encrusted with sessile creatures, its famous figurehead of Grainne Uaile turned to ruby coral...I hardly had time to mark its beauty when the beauty who held me turned us with a flip of her glittering tail, propelling us both down a hatch and into the captain's quarters...

'...which were laid out - well, fit for a king, or even a pirate captain. There was food. There was drink. More important to my bursting lungs, there was air rather than water to breathe. I looked at my merry-eyed companion and shrugged. We ate. We drank.

'There was a feather bed in the stateroom. Free of the sea, my companion displayed feet - very lovely ones - and a vivid imagination. I hope you have one, too, because that's all you're going to get of the naughty bit.

'Afterwards, I lay with my eyes closed, as she gently played with my hair. 'What makes you happy?' she murmured. 'What are you looking for? I will help you find it.'

'I shook my head. 'You can't, acushla,' I said with regret. 'I'm looking for something in the human heart...something few know is there...I can't share it, I can't teach it, but maybe...just maybe...I can leave a bit of a map as I go...'

'Her voice was wistful. 'Go make your map. And when you're done, come home to me. Take this to remember.' And just as I drifted off to sleep, I felt her slip something onto my finger...

'I woke to feel her caressing my hair still, but the light was too bright, I was feeling hot, and the featherbed had turned...sandy. When I opened my eyes, I was lying on a beach, the water lapping around my head. I sat up and looked around.

'I could see the yacht in the distance, so I knew they'd come and find me, maybe not in time for breakfast, but soon. I heard chattering in the trees, so I knew there were monkeys, perhaps even John Cleese. I sat dazed as the next wave brought me a gift: a waterproof bag. I opened it.

'Inside was a book - the complete works of WB Yeats, bookmarked with dried seaweed. I read the poem and laughed to myself. As I closed the book, I saw the ring on my little finger - gold, with a single, irregular pearl. To me, the rough pearl looked something like an apple.

The storyteller grins his crooked grin. 'That's the sophisticated part: Can you tell me what I read? If you want, read the works of Yeats until you find it, clever you - or you can come on deck later and tell me...' He glances at the croupier...'that it would make you happy if I quoted the poem to you. But maybe just a clue?'

He pats his breast pocket. 'I still have the map, you know. And of course I'm going back. What else would I be doing on a buck-, er, fine vessel such as the Nirvana? What do I want to do when I see my mermaid again? Return this, of course...'

And he holds up his right hand. On the little finger is a gold ring, the setting containing a single, large, irregularly-shaped pearl.

If you look carefully, it rather resembles an apple.