a locked door. there were no secret doors - the police have looked at every centimetre fo the floor , the ceiling , and the walls. And I also looked very carefully. So, no secret doors. what about the chimney? It is wide enough for a body for three metres, but higher up it is much narrower. Not even a cat could climb through it to the top. so what is left? 'the two windows,' I said. 'but they were fastened on the inside, weren't they?' 'yes, and no,' said dupin. 'let me explain. We can see all of the window on the left, you remember, but only the top half of the window on the right, because the head of the bed is pushed up next to thee window. the police tried to open the window on the left, but found a very strong nail in the wood, which stopped the window opening.