“It’s a poison to you,” my gran said thoughtfully, tapping an index finger against one tooth. “One that is compounding over the generations. Has it caused trouble other than mortality?”

Poison.

“Birth defects; madness; and, as is the case with the Duke, hemophilia,” Martin said. “Though some of it might be caused by inbreeding, particularly amongst the aristocracy.”

Gran wrinkled her nose. “Vile habit. And what of those with mixed blood: human and troll? Are they similarly afflicted?”

Martin shook his head. “There isn’t a single case of an afflicted half-blood on record; and for the thousands of years our kinds have intermingled, the life expectancy of half-bloods has remained constant. Injuries inflicted with steel weapons on half-bloods heal at approximately the same rate as those inflicted by other metals. If not for the marked decrease in power, the injection of human blood into our lines might have been a viable method of adapting ourselves to this world.”

I heard everything he said, but my mind was all for the word poison. “Gran,” I said. “How do you cure poisoning in humans? With magic, that is?”

“Depends,” she said. “Some poisons run their course quickly, and the magic cures the damage that has been done to the body. With others, the toxin lingers or builds, and the magic is used to draw it out of the body, which sometimes does more harm than good. It’s painful, and always more magic is required to heal the damage.”

“That’s it. The latter,” I said, my mind racing. “Do you know a spell?”

She nodded. “The best requires lobelia, but there will be none of that found in the dead of winter, so we will have to use alternatives. Regardless, it’s what needs doing afterward that’s the difficult part. But,” she eyed Martin, “you’ve told me time and again that the earth’s magic is ineffective on full-blooded trolls.”

“It is.” But what Martin had said about the earth using iron to rid itself of what didn’t belong had struck a chord. “A witch’s magic won’t work on them because they are not of this world,” I said. “But the iron is. What if the spell could be used to draw it out?”

“Surely it’s been tried?” Gran asked Martin, who shook his head. “Not that I’ve ever heard. Or if it has, it certainly didn’t work. ”

Excitement flooded through me, chasing away the cold and exhaustion. “It won’t hurt to try.”

Gran hissed softly between her teeth. “It will hurt. For better or worse, the iron is part of them now, has infiltrated every part of their bodies, even their magic. You’ll be tearing them apart to get it out.”

“And putting them back together with their own power,” I finished. There was a perfect symmetry to the idea. It felt right. “I want to try it.”

“Then you’ll need a test subject,” Martin said. “I propose that subject be me.”

I hesitated. He’d been through so much, and the thought of causing him more pain made my stomach sour. “Are you sure?”