The Dementor

Since I haven't posted anything in absolutely ages and I have given up on photography, I've decided to do some illustrations! This is the first one I've done, it's taken from Harry Potter and the Prisoner of Azkaban (my favourite of all the books/films )
The paragraph which I based my sketch on is below...

'Professor Lupin appeared to be holding a handful of flames. They illuminated his tired grey face, but his eyes looked alert and wary. "Stay where you are" he said, in the same hoarse voice, and he slowly got to his feet with his handful of fire held out in front of him.
But the door slid slowly open before Lupin could reach it. Standing in the doorway, illuminated by the shivering flames in Lupin's hand, was a cloaked figure that towered to the ceiling.'