I used the dryer spell to gently brush away dust and snow from the wall. It took me about a minute and a half, and when I was finished I caught another scent under the brimstone stench and said, "Double crap."
Murphy stepped forward with her flashlight and shone it on the wall.
The sigil had been painted on the wall in something thick and brown that smelled like blood. At first I thought it was a pentacle, but I saw the differences immediately.
"Harry," Murphy said quietly. "Is it human?"
"Most likely," I said. "Mortal blood is the strongest ink you can use for symbols like this in high-energy spells. I don't think anything else could have contained the amounts of energy it would have taken to blow up this building."
"It's a pentacle, right?" Murphy asked. "Like the one you wear."
I shook my head. "Different."
"How so?" Her mouth twitched at one corner. "Other than the blood, I mean."
"A pentacle is a symbol of order," I said quietly. "Five points, five sides. It represents the forces of air, earth, water, fire, and spirit. It's contained within a circle, the points touching the outer ring. It represents the forces of magic bound within human control. Power balanced with restraint." I gestured at the symbol. "See here? The points of the star fall far outside the ring."
She frowned. "What does it mean?"
"I have no idea," I said.
"Gosh," she said. "You're worth the money."
"Ha-ha. Look, even if I'd seen this symbol before, it could mean different things to different people. The Hindus and the Nazis have very different ideas about the swastika, for example."
"Can you make a guess?"
I shrugged. "Off the top of my head? This looks uncomfortably like a combination of the pentacle and the anarchy symbol. Magic unrestrained."
"Anarchist wizards?" Murphy asked.
"It's just a guess," I said. My gut told me it was a good one, though, and I got the impression that Murphy had the same feeling.
"What's the symbol for?" Murphy asked. "What is it meant to do?"
"Reflect power," I said. "My guess is that the energy that drove through the building was reflected from this sigil, which means..." I kayaked down a logic cascade as I spoke. "Which means that the energy had to come in from somewhere else first." I turned around slowly, trying to judge the angles. "The incoming beam must have gone right through the collapsed part of the building and-"
"Beam?"
I pointed at the semicircular hole in the ruined wall. "Yeah. Heat energy, a whole lot of it."
She studied the hole. "It doesn't look like it would be big enough to take down the building."
"It isn't," I said. "Not in an explosion, anyway. This just drilled a hole. Might have started a fire as it went, but it couldn't have sheared off the front of the building like that."
Murphy frowned, tilting her head. "Then what did?"
"Working on it," I mumbled. I judged the angles as best I could and took off down the alley. The firemen were still hard at work on the building, and we had to walk over several hoses as we emerged into the street at the back of the apartment building. I crossed the street and walked down the length of the building there, my hand raised, senses questing for any residual magic. I didn't find any, but I did smell Hellfire again, and a couple of feet later I found another not-pentacle, identical to the first, also hidden under a light dusting of snow.
I kept going clockwise around the ruined building. I found two more symbols on the undamaged building on its next side, and one more across the street from the front of the ruined apartments, and then I completed the circle, arriving back at our original reflective symbol.
Five reflection points, which had guided a truly freaking frightening amount of energy through the building, forming one single, enormous shape as they did.
"It's a pentagram," I said quietly.
Murphy frowned. "What?"
I touched the round, smooth bore mark on the destroyed building's wall. "The beam of energy that ripped through the building right here was one of five sides of a pentagram. A five-pointed star."
Murphy regarded me blankly.
I reached into my pocket and pulled out a piece of chalk. "Okay, look. Everyone learns to draw this in grade school, right?" I quickly sketched out a star on a clear bit of brick wall-five strokes of the chalk, forming five points. "Right?"
"Right," Murphy said. "You get them from the teacher when you get an A."
"Another example of symbols having disparate meanings," I said. "But look here, in the middle." I filled in the closed shape in the center of the star. "That's a pentagon shape, see? The center of the pentagram. That's where you contain whatever it is you're trying to contain."
"What do you mean, contain?"
"A pentagram like this one is a symbol of power," I said. "It's got a lot of uses, depending on how you employ it. But most often you use it to isolate or contain an entity."
"You mean like summoning a demon," Murphy said.
"Sure," I said. "But you can use it to trap other things too, if you do it right. Remember the circle of power at Harley MacFinn's place? Five candles formed the pentagram on that one."
Murphy shuddered. "I remember. But it wasn't this big."
"No," I admitted. "And the bigger you make it, the more juice it takes to keep it going. I've never, ever heard of one that would take this much energy to activate."
I drew little X shapes at the points of the star and drew the chalk from one to the next, thickening the lines of the example pentagram. "Get it? The beam streamed from one reflector to the next, melting holes through the building as it went. The reflectors formed the beam into one huge pentagram at ground level, more or less."
Murphy frowned and squinted at the simple diagram. "The center of that shape couldn't have covered the whole building."
"No," I said. "I'd need a good map to be sure, but I think the center of the pentagram must have been about twenty feet back from the front door. Which is why only the front half of the building collapsed."
"The explosion came from inside this pentagon thing? Magical TNT?"
I shrugged. "The explosion came from inside the pentagram's center, but not necessarily from the pentagram. I mean, it could have been a normal device of some kind."