“Actually, I have no objections to your drinking,” Hermione said, while Ron looked incredulous. “It’s just that you were doing a bit of talking last night…”
Ron and Harry have a bit too much butterbeer extra, and when Hermione goes to stop them, she hears something that shocks her. PostHBP. Thanks to Nephele de Tourmalin for the beauteous banner! Rox, she does.