Raven had said she was too cunning to use morphine or opium as the signs would be obvious: pinpoint pupils a clear indicator. Atropine dilated the pupils. Each drug counteracted the signs of the other.

Other things began to slot into place, other symptoms and signs that could now be explained: the thirst that Nora complained of at the Infirmary; the delirium, the muscle twitching, the grasping at phantoms that had afflicted other patients. All effects of excessive amounts of atropine.

As she hurried home, she thought about what she had learned about Mary Dempster: her following the apothecary around the wards of the Infirmary, her willingness to learn and her disregard for the prescribed doses of the medicines she administered. She was not using a poison as such, but killing her patients with excessive amounts of prescribed medicines.

Rounding the corner onto Albany Street, Sarah felt suddenly light-headed but put it down to the excitement of her revelation. As she opened her front door, however, she began to feel her legs give way. Staggering into the hallway, spots began to form at the periphery of her vision, fading to blackness as she collapsed onto the floor.

SIXTY-TWO

t was starting to rain as Raven contemplated the impressive front door of Quinton’s home on Castle Street, and he could not help but wonder what part a talent for forgery might have played in the book-keeper’s affording such a handsome address. It was not envy that had motivated him to come here, though; rather, his concern for a man who had no idea how deep and treacherous were the waters he was wading into.

It was Mrs Quinton who opened the door, a baby in her arms. The child looked sleepy, blinking at the light from the street, though Raven could not discern whether it was in the throes of waking up or nodding off.

From what he could see of the hallway behind her, the interior promised to be as grand as Sarah had described it. Raven wondered whether Quinton was not so new to the worlds of fraud and criminal enterprise, in which case his warnings were like to fall on deaf ears. Nonetheless, he was bound to try, and he had a duty to all at Queen Street.

‘This must be Rochester,’ he said, offering Mrs Quinton a broad smile.

She did not reciprocate and seemed wary of his familiarity.

‘Indeed. And you are?’

‘Dr Raven, assistant to Dr Simpson. I need to speak to your husband.’

She glanced behind briefly, then back at Raven, anxiety in her expression. He could tell she was thinking about telling him Quinton was not present, but she knew she had given herself away. One does not look to check when one knows someone is from home.

‘Now is not convenient,’ she said instead.

‘Believe me, the urgency of this matter trumps all convenience.’