Set in Stone, Chapter 10.

The darkroom smelled of hyposulphite and collodion, which was familiar, and of something else underneath that might have been his own apprehension, which was not. Darcy had given the plates two hours to settle before bringing them down. Long enough that dinner had been served and the household had dispersed to its evening occupations. Long enough that he would not be interrupted.

He lit the safety lamp and checked the solutions. Developer, stop bath, fixer: all as they should be. The two plates from this afternoon’s session were where he had left them, and he took the first with more care than strictly necessary.

The image emerged slowly. Elizabeth at three-quarters profile, her attention directed at the lens. The exposure had caught the line of her jaw and the set of her mouth, both suggesting something he could not quite name and did not particularly wish to.

He moved the plate to the stop bath and watched the development cease. The image was clear. Technically sound. He had been looking for micro-expressions, postural markers, any involuntary signal the body might offer before an episode. What he found instead was a woman looking at something beyond the frame with the kind of attention that suggested she was faintly amused by what he had asked her to do.

It told him nothing useful about the condition.

He fixed the plate and set it aside to dry, then worked his way through the second, third and fourth.

The fifth had been taken toward the end of the session, when she was starting to grow weary. She had relaxed slightly, not dramatically, but enough that the camera had noticed. The safety lamp’s red glow turned the wet plate strange and luminous as the image surfaced. She looked tired. She also looked—

He moved the plate to the stop bath and did not finish the thought.

The image was, again, technically sound. It showed her as she had been this afternoon: a woman sitting for a medical procedure she had not asked for, conducted by a man whose motives she was still deciding whether to trust. That it also showed her in a way that made him reluctant to look away was a problem of attention rather than content. The photographs themselves were entirely proper. It was his response to them that wanted management.

He fixed the plate. He set it beside the first. He looked at both of them longer than the clinical examination required, and told himself he was checking for artifacts in the emulsion.

The tripwire plates were still in their case at the back of the bench. One episode, four exposures: the mechanism had been triggered four times during her last sleepwalking incident, which had occurred six nights ago in the corridor outside the locked room. He had set the camera at the turn in the passage where the mirrors gave a safe line of sight. The flash powder had woken half the house. Elizabeth had woken in her own bed with no memory of having left it.

He had not yet developed the plates. There had been other matters requiring attention, and the household had needed careful management in the aftermath, and he had told himself there was no urgency.

He was not certain he believed himself.

He reached for the case, then stopped. The two plates drying on the rack showed Elizabeth as she was: present, alert, difficult in ways he was beginning to find less inconvenient than he ought. The tripwire plates would show her as she became when the condition took her.

He needed both sets of data. The human-form photographs were the baseline; the tripwire images were the deviation. Comparing them might yield something he had missed in previous cases. It was sound methodology.

He opened the case.

The red light turned the undeveloped glass into something that looked like pooled blood. He lifted the first plate carefully and moved toward the developer, and did not let himself think about what he expected to see when the image emerged.