big circle

Morgan sat in his wheelchair about forty feet away from Binder, my shotgun in his hands. Mouse stood beside the chair, focused intently upon Binder and his minions, his body tensed and ready to spring forward.
"Hello, Binder," Morgan said in a flat, merciless tone of voice. "Now, Miss Carpenter."
Molly appeared out of literally nowhere as she dropped the veil she'd been holding over herself since I'd first seen her moving at the beginning of the conversation with Binder. She was holding my spare blasting rod in her hand, its far end covered with pale dust from being dragged through the gravel. She knelt beside the long, lazy arc of the circle she'd drawn in the dust and touched her hand to it, frowning in concentration.
Circles of power are basic stuff, really. Practically anyone can make one if they know how to do it, and learning how to properly establish a circle is the first thing any apprentice is taught. Circles create boundaries that isolate the area inside from the magical energies of the world outside. That's why Binder's minions couldn't cross the plane of the circle I'd drawn on the ground-their bodies were made up of ectoplasm, held into a solid form by magical energy. The circle cut off that energy when they tried to cross it.
As it sprang to life at my apprentice's will, Molly's circle did the same thing as mine-only this time the grey suits were inside it. As the energy field rose up, it cut off the grey suits from the flow of energy they needed to maintain their solid forms.
And suddenly the next best thing to forty demonic thugs collapsed into splatters of transparent gook.
Binder let out a cry as it happened, spinning around desperately, mumbling some kind of incantation under his breath-but he should have saved himself the effort. If he wanted them back, he would have to get out of the isolating field of the enormous circle first, and then he would have to start from scratch.
"Ow, Binder," I said in patently false empathy. "Didn't see that one coming, did ya?"


Turn Coat Chapter 18, Page 169-170