Generally Cass didn't mind doing patrol rounds; they were quiet but not really boring, especially if he managed to get a partner that at least had a sense of humour. Unfortunately, he wasn't that lucky and was only too grateful to get away from that annoyance (who seemed more eager to scowl at him for no reason than doing the job).
He was almost at the common room entrance when he noticed the wall was already opening before he'd spoken the password. Seeing as it was after curfew that shouldn't have been happening at all, except for returning prefects.
"Y'know next time you want to sneak out you might want to check with Allegra first to see what the patrol schedule is," he suggests, after seeing Amy step past the wall.