"God, I'm sorry," I said. I got the car moving again.

Ash patted her chest and inspected her forehead in the mirror on the back of the sun-visor, using the torch she'd been reading with. "No lasting damage done, I think," she said, snapping the torch off and the visor shut.

"I'm really sorry," I said. I rubbed my hands on my trousers, one at a time. "I didn't mean —»

"Enough," Ash said. "I promise I won't sue, okay?"

"Yeah," I said, shaking my head. "But I'm really —»

"You think," Ash interrupted, "that your Uncle Fergus killed his wife by driving off the road and undoing her seat belt just before they hit?"

I took a deep breath. "Yes."

"Slow down, will you?" Ash said.

"Eh?" I said, slowing. We hadn't been going particularly fast.

Then I realised. "Oh. Yeah," I said, feeling even worse. "I pick my places, don't I?"

Ash didn't reply; we both watched, silent, as the Golf dawdled Past the parking place at the Cowal road junction where Darren Watt had died.

"Shit," I said. "Oh God, I'm doing an awful lot of apol —»

"Forget it," Ash said. "Let's get home."

I shook my head. "Oh shit," I said miserably.

The lights of Inveraray were off to our right, steady across the dark waters of Loch Shira as we rounded Strone Point, when Ash spoke again. "Bit of a risky way to top your wife, isn't it?"

"Convincing, though. And maybe… Don't laugh," I said, glancing over at her. "Maybe the perfect crime."

Ash looked at me dubiously. "Oh dear, Prentice. Really."

"I'm serious," I said. "He banged his head; he doesn't remember the last few miles of the drive. He even asked to be hypnotised, though they never did. Short-term memory gone, see? Hell, if he did it just on the spur of the moment, maybe even he isn't sure he meant it. He told me himself that he thought Fiona had been wearing a seat belt. I saw him just after the crash, while I was in hospital too, getting my appendix out. So nobody — maybe not even him — will ever know. It's fucking perfect. Risky but perfect, if it does work."

We stopped at traffic lights by the ornate, hump-backed bridge that took the road over the Aray. I sat staring at the red light; Inveraray sat ahead, round the side of the little bay, white buildings glowing in the sodium twilight of the street lights.

"But if he doesn't know he did it," Ash said, putting the sun visor down again and checking her forehead in the mirror in the lights of the on-coming stream of traffic, "why would he kill Rory anyway?"

I shrugged. "Maybe he does know he did it; but even if he doesn't, he might guess that he did. Maybe he was afraid Rory would publish something too close to the truth, maybe Rory was threatening to tell people about his theory; the police, for a start. Maybe neither murder was premeditated; maybe Fergus just reacted, both times. I don't know."

"Hmm," Ash said. She sat looking baffled for a bit, then shook her head. The lights changed and we crossed the bridge.

"If I'm right," I said, "Fergus probably had thought about killing her before he did. Maybe he only actually decided then and there, on the road that night; but he must have thought about it. Like I say; even if he isn't sure he did it himself, he knows he might have. I mean how hard do you have to think about something, how seriously, before it becomes something you could do, in the heat of the moment?"

"I give in," said Ash. "You tell me."

"Jeez," I said. "When I was feeling really bad last year I used to lie awake at night thinking that if there was some way of killing Lewis, quickly, painlessly, with no way of being found out, I might just do it, especially if I knew somehow that Verity would turn to me afterwards —»

"Oh for God's sake, Prentice," Ash said, turning her head to watch downtown Inveraray slide past. A minute later we were out, accelerating down the darkness of the loch side.

"Look," I said. "I was pretty fucked-up. I mean, I'm not saying it wasn't my own fault, Ash; I know it was. I'm not looking for sympathy. I'm just trying to explain that some crazy stuff can go through your head sometimes through love, or jealousy, and maybe, if it's triggered by something… I mean if somebody had actually given me a method of killing Lewis like that I'd probably have been horrified. I hope I couldn't even have thought about doing it any more once I knew it was possible. It was just a fantasy, a kind of warped internal therapy, something I day-dreamed about to make me feel better." I shrugged. "Anyway, that's the case for the prosecution."

Ash sat, mulling, for a while.

So," she said. "Have you checked out whether Fergus was alone the night Rory may or may not have gone to see him? I mean this whole thing falls to pieces if your uncle —»

"He was alone, Ash," I told her. "Mrs McSpadden had gone to visit relatives in Fife that weekend. Mum and dad had suggested the twins came and stayed with us. Fergus brought them over about tea time; I remember talking to him. He had a couple of drinks and then he left. So he was alone in the castle."

Ash looked at me. I just shrugged.

"Okay," she said eventually. She rested her elbow on the door, and tapped at her teeth with one set of nails. Her skirt had ridden up a little, and I stole the occasional glance at her long, blackly shining legs.

"So," she said later when we were in the forest, away from the loch side and a few kilometres out of Furnace. "What is to be done, Prentice?"

"I don't know," I confessed. "There's no body… Well, there is Aunt Fiona's, but that's neither here nor there. But Rory's still missing, in theory. I suppose I could go to the boys in blue with what I've got, but Jeez, can you imagine? Right, sonny, so you think this wee story that ye've read means yer uncle wiz kilt… Ah see. Would you mind just putting on this nice white jaikit? Aye, the sleeves are a wee bitty on the long side, but you won't be needing yer hands much in this braw wee room we've got for you with the very soft wallpaper."

We curved down into Furnace, the road finding the loch shore again. I could sense Ash looking at me, and chose not to look back, concentrating on checking the mirrors and the instruments. Eventually she took a breath. "Okay. Supposing Fergus did kill Rory, what did he do with the body?"

"Probably hid it," I said. "Not too near the castle… He had plenty of time; all night. He had a Land Rover; he could have got the bike in the back. Bit of a struggle maybe, but Fergus is a biggish lad, and a 185 Suzi isn't that heavy. It did occur to me he could have driven the bike himself with the body lashed to his back looking like a pillion. It's a bit Mezentian, but possible. But then he'd have had to have walked back from wherever he left it… " I looked over at Ashley, who was staring at me with a worried, even frightened expression. I shrugged. "But I think he took it up to one of the lochs in the hills, in the Landy; used the forestry tracks and dumped body and bike together into the water. There are plenty or places. The forest to the south of the castle, on the other side of the canal It's just full of little lochs up there, and there are tracks to most of them; it's the obvious… What's the matter?" I asked.

"You're right into all this, aren't you?"

"What do you expect?" I laughed, a strange, tight feeling in my belly. "What if I'm right? Jeez, this guy might just have killed two of my close relations; wouldn't you be kind of interested?"

Ash breathed out. "Oh dear, Prentice," she sighed, shaking her head and staring out of the window at the night as we swept through the forest towards Lochgair. "Oh dear, oh dear…»

We pulled up outside the Watt house in Bruce Street before eleven. Ash looked in the visor mirror again. She frowned and held her hair away from her face, turning her head from side to side. "Can't see a bruise," she said.