speaking to him we call him 'monsieur'; in speaking of him we call him 'the tall blonde.'"
"The tall blonde!" repeated M. Paul.
"Exactly. He has been here several times with a woman he calls Anita. That's all I know about it. Anyway, what difference does it make since he didn't come to-night?"
"How do you know he didn't come? He had a key to the alleyway door, didn't he?"
"Yes, but I tell you he sent a petit bleu."
The detective shrugged his shoulders. "Some one has been here and locked this door on the inside. I want it opened."
"Just a moment," trembled Gritz. "I have a pass key to the alleyway door. We'll go around."
"Make haste, then," and they started briskly through the halls, the proprietor assuring M. Paul that only a single key was ever given out for the alleyway door and this to none but trusted clients, who returned it the same night.
"Only a single key to the alleyway door," reflected, Coquenil.
"Yes."
"And your 'tall blonde' has it now?"
"I suppose so."
They left the hotel by the main entrance, and were just going around into Rue Marboeuf when the concierge from across the way met them with word that Cæsar had arrived.
"Cæsar?" questioned Gritz.
"He's my dog. Ph-h-eet! Ph-h-eet! Ah, here he is!" and out of the shadows the splendid animal came bounding. At his master's call he had made a mighty plunge and broken away from Papa Tignol's hold.
"Good old fellow!" murmured M. Paul, holding the dog's eager head with his two hands. "I have work for you, sir, to-night. Ah, he knows! See his eyes! Look at that tail! We'll show 'em, eh, Cæsar?"
And the dog answered with delighted leaps.
"What are you going to do with him?" asked the proprietor.
"Make a little experiment. Do you mind waiting a couple of minutes? It may give us a line on this visitor to Number Seven."
"I'll wait," said Gritz.
"Come over here," continued the other. "I'll show you a pistol connected with this case. And I'll show it to the dog."
"For the scent? You don't think a dog can follow the scent from a pistol, do you?" asked the proprietor incredulously.
"I don't know. This dog has done wonderful things. He tracked a murderer once three miles across rough country near Liége and found him hidden in a barn. But he had better conditions there. We'll see."
They had entered the courtyard now and Coquenil led Cæsar to the spot where the weapon lay still undisturbed.
"Cherche!" he ordered, and the dog nosed the pistol with concentrated effort. Then silently, anxiously, one would say, he darted away, circling the courtyard back and forth, sniffing the ground as he went, pausing occasionally or retracing his steps and presently stopping before M. Paul with a little bark of disappointment.
"Nothing, eh? Quite right. Give me the pistol, Papa Tignol. We'll try outside. There!" He pointed to the open door where the concierge was waiting. "Now then, cherche!"
In an instant Cæsar was out in the Rue Marboeuf, circling again and again in larger and larger arcs, as he had been taught, back and forth, until he had covered a certain length of street and sidewalk, every foot of the space between opposite walls, then moving on for another length and then for another, looking up at his master now and then for a word of encouragement.
"It's a hard test," muttered Coquenil. "Footprints and weapons have lain for hours in a drenching rain, but—Ah!" Cæsar had stopped with a little whine and was half crouching at the edge of the sidewalk, head low, eyes fiercely forward, body quivering with excitement. "He's found something!"
The dog turned with quick, joyous barks.
"He's got the scent. Now watch him," and sharply he gave the word: "Va!"
Straight across the pavement darted Cæsar, then along the opposite sidewalk away from the Champs Elysées, running easily, nose down, past the Rue François Premier, past the Rue Clement-Marot, then out into the street again and stopping suddenly.
"He's lost it," mourned Papa Tignol.
"Lost it? Of course he's lost it," triumphed the detective. And turning to M. Gritz: "There's where your murderer picked up a cab. It's perfectly clear. No one has touched that pistol since the man who used it threw it from the window of Number Seven."
"You mean Number Six," corrected Gritz.
"I mean Number Seven. We know where the murderer took a cab, now we'll see where he left the hotel." And hurrying toward his dog, he called: "Back, Cæsar!"
Obediently the dog trotted back along the trail, recrossing the street where he had crossed it before, and presently reaching the point where he had first caught the scent. Here he stopped, waiting for orders, eying M. Paul with almost speaking intelligence.
"A wonderful dog," admired Gritz. "What kind is he?"
"Belgian shepherd dog," answered Coquenil. "He cost me five hundred francs, and I wouldn't sell him for—well, I wouldn't sell him." He bent over and fondled the panting animal. "We wouldn't sell our best friend, would we, Cæsar?"
Evidently Cæsar did not think this the moment for sentiment; he growled impatiently, straining toward the scent.
"He knows there's work to be done and he's right." Then quickly he gave the word again and once more Cæsar was away, darting back along the sidewalk toward the Champs Elysées, moving nearer and nearer to the houses and presently stopping at a gateway, against which he pressed and whined. It was a gateway in the wall surrounding the Ansonia Hotel.
"The man came out here," declared Coquenil, and, unlatching the gate, he looked inside, the dog pushing after him.
"Down Cæsar!" ordered M. Paul, and unwillingly the ardent creature crouched at his feet.
The wall surrounding the Ansonia was of polished granite about six feet high, and between this wall and the hotel itself was a space of equal width planted with slim fir trees that stood out in decorative dignity against the gray stone.
"This is what you call the alleyway?" questioned Coquenil.
"Exactly."
From the pocket of his coat the detective drew a small electric lantern, the one that had served him so well earlier in the evening, and, touching a switch, he threw upon the ground a strong white ray; whereupon a confusion of footprints became visible, as if a number of persons had trod back and forth here.
"What does this mean?" he cried.
Papa Tignol explained shamefacedly: "We did it looking for the pistol; it was Gibelin's orders."
"Bon Dieu! What a pity! We can never get a clean print in this mess. But wait! How far along the alleyway did 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, Cæsar! Cherche!"
Once more the eager animal sprang forward, following slowly along the row of trees