Carstairs nodded encouragingly. He reminded Lindsay of her Latin teacher, another ugly, skinny man who’d been nicknamed Plug because of his lack of physical charms. But he’d been a kind teacher, who had always managed to draw out even those most lacking in confidence. Feeling reassured, Lindsay went on. “The glass,” she said. “It doesn’t fit.”

“Well spotted,” Carstairs said with an air of genuine delight at her perspicacity.

“And the police don’t seem to have bent over backward to try to find out who the mysterious thumbprint belongs to,” she went on.

“Good. Of course, I needn’t tell you that pursuing that course of inquiry was virtually impossible for us. After all, I have no authority to go round fingerprinting people. With the whole population of Glasgow to go at, and no real suspects other than Jackie, we couldn’t begin to unearth the owner of the print. If there had been someone else who had been an obvious suspect, we could have got their prints by some subterfuge, I suppose. But neither Claire nor I had the foggiest idea where to begin,” he apologized. “However, from what I’m told, which squares with what I understand about fingerprinting techniques, it’s likely that the print had been made that day. They certainly weren’t the sort of residual prints that might have been left after the glass had been washed,” he continued enthusiastically.

“Who did the police fingerprint?” Lindsay asked, mildly irritated by Carstairs’ failure to pursue the one lead that he and Claire had to the real culprit. God preserve me from falling into the hands of lawyers, she thought to herself.

“No one, really. They had no evidence apart from the glass that anyone else had been there. No one else had been seen or heard. Mrs. Makaronas from the flat upstairs heard Jackie and Alison quarreling, but that was all she admitted to having heard.”

“Would that be Ruth Menzies? The gallery owner?” Lindsay interrupted.

“That’s right. A friend of the dead woman. Retains her maiden name professionally. Not a very helpful witness from our point of view. Now, as I was saying, the only direct evidence was the glass, and they didn’t fingerprint all her friends and associates. In fact, they didn’t even look too hard for her friends and etceteras, as you’ll probably have picked up from the case file.”

Lindsay shook her head doubtfully. “It’s not much to go at. But at least it’s a start. I was beginning to wonder if we were all wrong, and that maybe Jackie had actually done it, in spite of everything my instincts tell me about her and about this crime.”