you look?"

"As far as that back wall. Poor Gibelin! He never thought of looking on the
other side of it. Eh, eh!"

Coquenil breathed more freely. "We may be all right yet. Ah, yes," he
cried, going quickly to this back wall where the alleyway turned to the
right along the rear of the hotel. Again he threw his white light before
him and, with a start of satisfaction, pointed to the ground. There,
clearly marked, was a line of footprints, _a single line_, with no breaks
or imperfections, the plain record on the rain-soaked earth that one
person, evidently a man, had passed this way, _going out_.

"I'll send the dog first," said M. Paul. "Here, Caesar! _Cherche!_"

Once more the eager animal sprang forward, following slowly along the row
of trees where the trail was confused, and then, at the corner, dashing
ahead swiftly, only to stop again after a few yards and stand scratching
uneasily at a closed door.

"That settles it," said Coquenil. "He has brought us to the alleyway door.
Am I right?"

"Yes," nodded Gritz.

"The door that leads to Number Seven?"

"Yes."

"Open it," and, while the agitated proprietor searched for his pass key,
the detective spoke to Tignol: "I want impressions of these footprints, the
_best_ you can take. Use glycerin with plaster of Paris for the molds. Take
_this_ one and these two and _this_ and _this_. Understand?"

"Perfectly."

"Leave Caesar here while you go for what you need. Down, Caesar! _Garde!_"

The dog growled and went on guard forthwith.

"Now, we'll have a look inside."

The alleyway door stood open and, using his lantern with the utmost care,
Coquenil went first, mounting the stairs slowly, followed by Gritz. At the
top they came to a narrow landing and a closed door.

"This opens directly into Number Seven?" asked the detective.

"Yes."

"Is it usually locked or unlocked?"

"IT is _always_ locked."

"Well, it's unlocked now," observed Coquenil, trying the knob. Then,
flashing his lantern forward, he threw the door wide open. The room was
empty.

"Let me turn up the electrics," said the proprietor, and he did so, showing
furnishings like those in Number Six except that here the prevailing tint
was pale blue while there it was pale yellow.

"I see nothing wrong," remarked M. Paul, glancing about sharply. "Do you?"

"Nothing."

"Except that this door into the corridor is bolted. It didn't bolt itself,
did it?"

"No," sighed the other.

Coquenil tho