What's the time reference for this would?

Question

A lamp flickered on. It was Hermione Granger, wearing a pink bathrobe and a frown.
"You!" said Ron furiously. "Go back to bed!"
"I almost told your brother," Hermione snapped, "Percy –– he's a prefect, he'd put a stop to this."

–– Harry Potter and the Sorcerer's Stone

The highlighted part, I would say, has different Reference Times: telling’s RT is the past; put’s RT is after the Speech Time. If this is true, I can imagine this sentence: ‘If I told him what you’re going to do, he’d put a stop to this’. Is it right?

Answer 1

I think you have it exactly right. It’s a present-tense threat: Hermione is making it very clear to her friends that although she did not tell Percy earlier she still could tell him, and if she did tell him he would put a stop to activities of this sort.