will vs demon

"You really shouldn't just hand someone else a demon's name," I told him. Then I drew in a breath, and shouted out in a voice of command, "Kalshazzak!"
The demon stopped in its tracks and gave a whistling howl of agony and rage as I called its name and drew my will up to hurl against it.
"Kalshazzak," I snarled again. The demon's presence was suddenly there, in my head, raging slippery and slimy and wriggling like a venomous tadpole. It was a pressure, a horrible pressure on my temples that made me see stars and threatened to steal enough of my balance to send me falling to the floor.
I tried to speak again and the words stuck in my throat. The demon hissed in anticipation, and the pressure on my head redoubled, trying to force me down, to make me give up the struggle, at which point the demon would be free to act. The lightning blue of its eyes became glaringly bright, painful to look upon.
I thought of little Jenny Sells, oddly enough, and of Murphy, lying pale and unconscious on a stretcher in the rain, of Susan, crouched next to me, sick and unable to run.
I had beaten this frog once. I could do it again.
I cried out the demon's name for the third and final time, my throat burning and raw. The word came out garbled and imperfect, and for a sinking moment I feared the worst, but Kalshazzak howled again, and hurled itself furiously to the floor, thrashing its limbs about like a poisoned bug, raging and tearing great swaths out of the carpet. I sagged, the weariness that came over me threatening to make me black out.


Storm Front Chapter 26, Page 294