"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. Now these iron blinds have remained fastened
by their iron latch; and yet we have proof that the murderer made
his escape from the, pavilion by that window! Traces of blood on
the inside wall and on the blinds as well as on the floor, and