There's a kind of mathematics that goes along with saving people's lives. You find yourself running the figures without even realizing it, like a medic on a battlefield. This patient has no chance of surviving. That one does, but only if you let a third die.

For me, the equation broke down into fairly simple elements. The demon, hungry for its revenge, would come after those who had struck it down. The ghost would only remember those who had been there, whom it had focused on in those last moments. That meant that Murphy and Michael would be its remaining targets. Michael had a chance of protecting himself against the thing-hell, maybe a better chance than me. Murphy didn't.

I got on the phone to Murphy's place. No answer. I called the office, and she answered with a fatigue-blurred, "Murphy."

"Murph," I said. "Look, I need you to trust me on this one. I'm coming down there and I'll be there in about twenty minutes. You could be in danger. Stay where you are and stay awake until I get to you."

"Harry?" Murphy asked. I could hear her starting to scowl. "You telling me you're going to be late?"

"Late? No, dammit. Look, just do what I said, all right?"

"I do not appreciate this crap, Dresden," Murphy growled. "I haven't slept in two days. You told me you'd be here in ten minutes, and I told you I'd wait."

"Twenty. I said twenty minutes, Murph."

I could feel her glare over the phone. "Don't be an asshole, Harry. That's not what you said five minutes ago. If this is some kind of joke, I am not amused."

I blinked, and a cold feeling settled into my gut, into the hollow place the Nightmare had torn out of me. The phone line snapped, crackled, and popped, and I struggled to calm down before the connection went out. "Wait, Murphy. Are you saying you talked to me five minutes ago?"

"I am about two seconds short of killing the next thing that pisses me off, Harry. And everything keeping me out of bed is pissing me off. Don't get added to the list." She hung up on me.

"Dammit!" I yelled. I hung up the phone and dialed Murphy's number again, but only got a busy signal.

Something had talked to Murphy and convinced her she was talking to me. The list of things that could put on someone else's face was awfully long, but the probabilities were limited: either another supernatural beastie had wandered onto the stage or, I gulped, the Nightmare had taken a big enough bite of me that it could put on a convincing charade.