Draco's eyes went wide with surprise, and a little fear, but he'd been face to face with the Dark Lord's fury, he was a professor at Hogwarts, he didn't flinch anymore. He had a responsibility. His wand was in his hand before he could blink, and he pushed past the urge to cast Stupefy and instead cast Immobilus from the hip, the spell that had stopped the dark creature from the library in its tracks.