Draco was the first to realise Granger was missing. Weasley had said something again that afternoon and she hadn’t been seen since—he’d figured she needed some space, but what with a troll stomping around…
He didn’t wait for the teachers—there wasn’t any time, he figured, and he was right. Just as he passed the girl’s toilets, he saw it, the troll, huge and hideous, and he cautiously walked up there.
The troll was in the process of smashing everything in his vicinity with a huge club, including Granger; yet when she saw him, she was already yelling what to do, having seemingly lost her own wand. And for once he didn’t contradict her, but went along with what he realised was her idea.
He didn’t get to be the hero every day.