Knocking at a window. Literally.
Wan saw the Dark Mark explode across the sky as he lay stretched out on the roof of Ravenclaw tower. It was late, a couple hours after night had fallen, and he'd been enjoying the peace of view afforded him. The stars were clear and the sounds of the world faded away behind the roar of the wind. He could almost fall asleep up there, except that it was actually starting to get cold.
He figured he could stay out another hour or so before he used the school broom he'd accio'd up earlier to get down. Jumping in the dark was more risk than he wanted to take. The broom was forgotten as the sky lit up in the ugly green and the message to get to the nearest common room rang loudly in his ears.
Wan's first instinct was not to grab the broom, but to instead flip himself off the edge of the roof and find his way down to the nearest window. Which was how he found himself sitting on the stone outcropping just outside one of the Ravenclaw common room's windows. He really hoped someone would hear his knocking because he did not want to lose 100 points for his house just because he couldn't get inside the common room.