Fulgurite is a natural glass, like another of the museum's minor treasures, obsidian. But while obsidian is born purely of the earth, formed in the baking heat and furious pressure of volcanic eruptions, fulgurite is of the earth and of the air, too; it is made when lightning strikes unconsolidated sand, and fuses it, vitrifies it in long, zig-zag tubes. God's glass, Hamish McHoan called it.

The Gallanach Glass Works Museum contained a collection of tubular fulgurites, plucked from the sands of Syria by Walter Urvill — Fergus's grandfather — on a visit there in 1890, and transported back to Scotland with great care and not a little luck so that they arrived intact. One of the crinkled, gnarled little tubes was over a metre long; another just a fraction shorter. Fergus had the smaller of the two sent to a jeweller in Edinburgh, to be broken, the pieces graded and ground and polished and threaded together like dark little pearls, to create a unique necklace for his niece.

He presented the result to the lightning-child during ner birthday party, at her parents" house in Merchiston, in Edinburgh, in August 1988 (it was, perhaps unfittingly, a perfectly fine, warm, clear and calm night, on that anniversary). Fergus — always a rather dour, prematurely elderly figure, characterised by those collar-contacting jowls — improved immensely in the eyes of both Kenneth and Prentice McHoan with that single, elegant, and rather unexpectedly poetic act.

Verity had the grace to accept the necklace with a particular gratitude that acknowledged the thought behind the gift, and the taste to make it a regular, even habitual, part of her wardrobe.

The upholstery of Fergus's Rover was cleansed of the debris and stains associated with Verity's birth and the car continued to serve the Urvill family for another five years or so until 1975, when it was traded in (for what Prentice would thereafter maintain was a scandalously small sum, considering that the thing ought to have been preserved as some sort of internationally-recognised shrine to Beauty) for an Aston Martin DB6.

It was once Prentice's dream, shortly after he'd passed his driving test, to find that old Rover — lying in a field somewhere, perhaps — and to buy it; to own the car his beloved had been born in; to drive it and to cherish it. He realised, of course, that it had almost certainly been scrapped long before, but that had not prevented him harbouring the perhaps irrational notion that somehow a little of its recycled metal must have found its way into at least one of the three old bangers he'd owned.

The defiantly thunderous and lightning-fast Aston Martin DB6 was the car that Fergus and Fiona Urvill were travelling in on the night they were involved in a crash at Achnaba, just south of Lochgair, in 1980.

Right, now this isn't as bad as it sounds, but… I was in bed with my Aunty Janice.

Well, actually, in one sense it's exactly as bad as it sounds because when I say I was in bed with her, I don't mean I was in bed with her because we'd gone hill-walking together and been caught out in a snow storm and eventually found shelter in some exceptionally well-appointed bothy that just so happened to have only one bed and we had to get into it together to keep warm; nothing like that. We were fucking.

But (phew), she wasn't a real aunt; not a blood relation, not even an aunt by marriage. Janice Rae had been Uncle Rory's girlfriend, and I just called her Aunty. However she had been my father's brother's lover, and — perhaps more embarrassingly — it had been her daughter, Marion, who had initiated me into the whole sticky, smelly, noisy, potentially fatal, potentially natal, sordid and sublime act in the first place, on the dry, cracked green leather surface of the garaged Lagonda Rapide Saloon's back seat, one hot and musty summer's afternoon, eight years earlier. (We brought the house down.) Blame Lewis.

The voice has gone quiet, deep, almost gravelly now. A light — harsh and white — shines from one side, so that his lean, cleanshaven face looks hard and angular, even cruel.

"I have this door in my house," he breathes, then pauses. "It's a very special door." He looks to one side. The way he does it, you get the urge to look that way too, but you don't. "Do you know what I keep on the other side of that door?" He raises one eyebrow, but there is silence in the darkness. You wait. "Behind the door I keep… " (He leans forward now, towards us, somehow confiding and threatening together.) "… the rest of the Universe." A wintery smile, and if you were prone to that sort of thing, your skin might crawl.

There is a little nervous laughter. He waits patiently for it to subside. "I have a special name for that door," he says, eyes narrowing. "Do you know what I call it?" (This is the dangerous bit, where it could all end in disaster, but he holds the pause, and the silence is eloquent.) "I call it… " he pauses again, looks into the darkness to one side, then towards the light again."… my Front Door."

There is more laughter, like relief. He smiles for the first time; a thin, unimpressed expression. "Perhaps you have one like it, in your house." He steps back, the lights go up, and he makes a sort of half nod, half bow. "My name is Lewis McHoan. Good night."

He walks off to loud applause; cheers, even.

I look from the television to my flatmates.

"Aye, he's no bad," Gav says, pulling open another can of cider.

"He's okay," agrees Norris, and drinks from his. "That last bit was a bit weird but. He really your brother, aye?"

I glare at the screen as the MC appears, signing off. Lewis had been the last act. "Yes." I say, taking my empty Export can between both hands, and crushing it. "Yes, he is." The credits roll. I throw the squashed can at the litter bin, but it misses, hits the wall, rolls across the floor and dribbles flat beer onto the threadbare carpet.

I stood in the bookshop, reading the story about the magic dressing gown, tears in my eyes.

A hand tapped me on the shoulder. I put the book down quickly on the pile and hauled my hanky from my pocket, bringing it up to my face as I turned. I blew my nose.

"Come on, slow-coach," mum said, smiling down at me. Her gaze flicked to the book-pile. "Reading your dad's stories at last, eh? What's brought this on?" Not waiting for an answer, she put one arm round my shoulders and guided me out onto the Departures concourse. "Come on; let's go and wish your Uncle Rory bon voyage, shall we?"

"All right," I said, sniffing.

Mum frowned down. "Prentice, have you been crying?"

"No!" I said vehemently, shaking my head and stuffing the hanky back into my trousers. Mum just smiled. I felt the tears try to come again, prickling behind my eyes.

"Prentice!" Uncle Rory said, picking me up. "God, you're getting big. I'll soon not be able to lift you."

Good, I thought; this is embarrassing. I hugged him, as much to get my face out of sight as to express any regret at his leaving.

"Aye," I heard my mum saying. "I think we had a wee tear or two, there."

"We didn't, did we?" Uncle Rory laughed, bringing me back round in front of him, holding me there. His big face, entirely framed by curly auburn hair, looked happy and kindly. I wanted to hit him and my mum, or maybe burst into tears and hug them; either would do. "Ah, dinnae greet, laddy," he laughed, lapsing into the working-class Scots I had grown ashamed of because my beautiful cousins Diana and Helen didn't speak like that, and those coarse Watt children did.

Stop it! I beamed at him (I was trying to develop a technique for aiming my thoughts at people to get them to do things for me; there were promising developments, but it was early days still, and I was suffering a lot of teething problems. That bastard George Lucas hadn't had the decency to reply to my letter about The Force yet, either).