“Our cages were…” She swallows. Such bitterness in her throat! “Our cages were pushed together. We could whisper. We could reach out and touch each other’s hands.”

“I could reach out from my cage and touch your hand right now.”

Her eyes flash and her voice firms. “Don’t.”

“Our friend in Pennsylvania doesn’t keep his donors in cages. How does he control them?”

That flash of fire has cleared some of the clouds in her head. “Ether. He knocks them out with ether.”

“Hmm. But I don’t think he would want them etherized at the end. He would want the drug out of their blood, because the blood is too important.”

“How do you know?”

He smiles. “Let’s just say I have a fellow feeling with our new friend. I don’t think he would want any impurities in the blood. I’m sure he wants his donors clean and sober for the grand finale. Have you checked the histamine levels?”

“Yes. We couldn’t make sense of the numbers.”

“We?”

She corrects herself without stumbling. “Me. Agent Cooper just gave me the file—he didn’t offer to translate it. I have numbers but I don’t know what they mean.”

“Then allow me to explain. In postmortem biochemistry, if the free histamine reference range is over thirty-five but not less than twenty-two nanograms per milliliter, the subject was in distress.”

Sweat on her brow, her own distress. “Why doesn’t the killer want impurities like ether in the victims’ blood?”

“He’s been particular up until now, hasn’t he. He’s cleaned off prints, removed clothes to avoid fiber contamination, disposed of ropes. He’s a very tidy fellow.”

“And the blood is too important.”

“Oh, Emma—the blood is everything.” Simon’s shoulders straighten as he elaborates. “It’s his purpose, his essence, his reason for all this. I imagine he loses himself a little when the red is all around him. It’s so easy to get carried away in the moment.”

“Does he need a special sort of blood? How does he know he’s got the right donor?”

“That’s an interesting question. Have you ever selected fruit at the greengrocer? You squeeze a little to see if it’s ripe, ask for a slice so you can nibble—taste is very individual.”

“Is he taste-testing them?” Urgency in her voice now. “Simon, how is he choosing his victims?”

He grins. “Another good question. Pick at it a little, I’m sure it will come to you.”

It does come, like the pulsing scarlet blaze of a ship’s flare. “He knows their blood type.”

“It’s more than just blood type, though. He sees something glowing in them, something he wants to kindle inside himself.” Simon’s own eyes are glowing. “It’s like the gleam of a firefly.”

“What is it?”

“Listen. No man chooses evil because it is evil; he only mistakes it for happiness, the good he seeks—Mary Shelley, of course. Our Pennsylvania friend seeks his happiness. Every creature on earth has wants and desires, has things they turn toward—flower to sun, snake to warmth, moth to flame. Daniel Huxton saw something in you, Emma. He could not resist your shine.”