Re: Knocking at a window. Literally.
Russell hurried to the common room of Ravenclaw tower. The Dark Mark hanging in the sky and the groups of Deatheaters attacking the castle filled him with dread. He had to get the students gathered to the common room quickly and take an accounting of his Ravenclaws.
When he got there, he was startled by a figure in the window tapping on the glass. He recognized the student and opened the window quickly and helped him in. "Come in," he said. "The school is being locked down. You'll have to stay here in Ravenclaw."