They left the pub and returned to the car for the second piece of timed driving. Lindsay drove the car to its limits and they shot into the drive a bare seven minutes later.

“I have the beginnings of a theory, thanks to you working out the times,” Lindsay mused, cutting the engine. “Cartwright saw her sorting out strings, he says. Now, suppose she left them lying around in the room. He could fairly assume she’d be back there before she went on stage.

“He could have had a quick one in the Woolpack, raced back to the school, left his car in the trees beyond the houses, got the toggle from Longnor—after all, no one would have thought anything of seeing him there with Sarah doing her Greta Garbo routine. A quick dash through the trees to the main building. In by the side door, up the back stairs, and into Music 2. He’d have had to go back home in the afternoon to pick up the school keys, by the way—I imagine he’s got a set. Then he picks up a string—he’s good with his hands, and strong. Then it’s into the walk-in cupboard till Lorna arrives. As soon as Paddy goes, he’s out and strangling her with one of the strings she’s so conveniently left lying around. Then he’s off, down the back stairs, drives like a madman, and is back in the Stonemason’s by five to eight. It could be done.”

Cordelia looked doubtful. “It has its points. But you’re assuming he has a set of keys. You’re also assuming he could figure out her movements. I mean, it could have happened that Lorna didn’t come into the room until just before she went on—he could have been stuck in the cupboard for over an hour, and where would his alibi have been then? And how the hell do we prove any of it?”

“You forget, we don’t actually have to prove anything. We’re not policemen, having to stand everything up in court. All we really have to do for Paddy’s purposes is to demonstrate that she’s far from being the only person with motive, means, and opportunity.”

“I suppose so. I rather like the thought of Cartwright as First Murderer. He could have given himself a bit more time by making his preparations in the afternoon—making the garrote and all that. He couldn’t be sure he’d get there ahead of Lorna, but it was a reasonable assumption. And the confusion over Margaret Macdonald’s keys could simply be a fortuitous red herring.”