As Coquenil listened, his mouth drew into an ominous thin line and his deep eyes burned angrily.

“M.  Gritz,” he said in a cold, cutting voice, “you are a man of intelligence, you must be.  This crime was committed last night about nine o’clock; it’s now half past three in the morning.  Will you please tell me how it happens that this fact of vital importance has been concealed from the police for over six hours?”

“Why,” stammered the other, “I—­I don’t know.”

“Are you trying to shield some one?  Who is this man that engaged Number Seven?”

Gritz shook his head unhappily.  “I don’t know his name.”

“You don’t know his name?” thundered Coquenil.

“We have to be discreet in these matters,” reasoned the other.  “We have many clients who do not give us their names, they have their own reasons for that; some of them are married, and, as a man of the world, I respect their reserve.”  M. Gritz prided himself on being a man of the world.  He had started as a penniless Swiss waiter and had reached the magnificent point where broken-down aristocrats were willing to owe him money and sometimes borrow it—­and he appreciated the honor.

“But what do you call him?” persisted Coquenil.  “You must call him something.”

“In 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 Caesar had arrived.

“Caesar?” 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, Caesar?”