Mademoiselle Stangerson had no need for one, since Daddy Jacques lodged in the pavilion and because, during the daytime, she never left her father.

When they, all four, rushed into The Yellow Room, after breaking open the door of the laboratory, the door in the vestibule remained closed as usual and, of the two keys for opening it, Daddy Jacques had one in his pocket, and Monsieur Stangerson the other.
As to the windows of the pavilion, there are four; the one window of The Yellow Room and those of the laboratory looking out on to the country; the window in the vestibule looking into the park." "It is by that window that he escaped from the pavilion!" cried Rouletabille.
"How do you know that ?" demanded Monsieur de Marquet, fixing a strange look on my young friend.
"We'll see later how he got away from The Yellow Room," replied Rouletabille, "but he must have left the pavilion by the vestibule window." "Once more,--how do you know that ?" "How?
Oh, the thing is simple enough! As soon as he found he could not escape by the door of the pavilion his only way out was by the window in the vestibule, unless he could pass through a grated window.

The window of The Yellow Room is secured by iron bars, because it looks out upon the open country; the two windows of the laboratory have to be protected in like manner for the same reason.

As the murderer got away, I conceive that he found a window that was not barred,--that of the vestibule, which opens on to the park,--that is to say, into the interior of the estate.

There's not much magic in all that." "Yes," said Monsieur de Marquet, "but what you have not guessed is that this single window in the vestibule, though it has no iron bars, has solid iron blinds.