The panel slides back and you enter a room which main feature is a huge mirror, or perhaps it is a window. In any case, it is easy to see that someone is trapped behind that window. You can't quite make out who the person is at first, but as you get closer you realize that the person in danger appears to be your Head of House, Professor Shackleton. This is not good!

You will notice that there are two doors here, one of which will return you to the school. This is the door on the left. But if you choose the other door, the one on the right, you can choose to stay and help your professor.