prevents Lash from leaving

The fallen angel turned to depart on that note, probably because it would have made a nicely scary exit line.
I extended my hand, and with it my mind, and barred her departure with an effort of simple will. Lasciel existed only in my thoughts, after all. "My head," I told her. "My rules. We aren't finished."
She turned to face me, and her eyes suddenly glowed with orange and amber and scarlet flickers of Hellfire. It was the only non-black thing about her.
"See, here's the thing," I said. "My inner evil twin might have a lot of impulses I'd rather not indulge - but he isn't a stranger. He's me."


White Night Chapter 33, Page 335