man.  His imagination told him that the person who committed this crime had suggested the manner of it, and overseen the details of it down to even the precise placing of the eye holes.  It must be so or the plan would not have succeeded.  The assassin, then, was a friend of Martinez—­that is, the Spaniard had considered him a friend, and, as it was of the last importance that these holes through the wall be large enough and not too large, this friend might well have seen personally to the purchase of the auger, not leaving it to a rattle-brained billiard player who, doubtless, regarded the whole affair as a joke.  It was not a joke!

So, as part of his day’s work, M. Paul had taken steps for the finding of this smallish object dropped into the Seine by Pussy Wilmott, and, betimes on the morning after that lady’s examination, a diver began work along the Concorde bridge under the guidance of a young detective named Bobet, selected for this duty by M. Paul himself.  This was one thread to be followed, a thread that might lead poor Bobet through weary days and nights until, among all the hardware shops in Paris, he had found the particular one where that particular auger had been sold!

Another thread, meanwhile, was leading another trustworthy man in and out among friends of Martinez, whom he must study one by one until the false friend had been discovered.  And another thread was hurrying still another man along the trail of the fascinating Anita, for Coquenil wanted to find out why she had changed her mind that night, and what she knew about the key to the alleyway door.  Somebody gave that key to the assassin!

Besides all this, and more important, M. Paul had planned a piece of work for Papa Tignol when the old man reported for instructions this same Wednesday morning just as the detective was finishing his chocolate and toast under the trees in the garden.

“Ah, Tignol!” he exclaimed with a buoyant smile.  “It’s a fine day, all the birds are singing and—­we’re going to do great things.”  He rubbed his hands exultantly, “I want you to do a little job at the Hotel des Etrangers, where Kittredge lived.  You are to take a room on the sixth floor, if possible, and spend your time playing the flute.”

“Playing the flute?” gasped Tignol.  “I don’t know how to play the flute.”

“All the better!  Spend your time learning!  There is no one who gets so quickly in touch with his neighbors as a man learning to play the flute.”

“Ah!” grinned the other shrewdly.  “You’re after information from the sixth floor?”

M. Paul nodded and told his assistant exactly what he wanted.

“Eh, eh!” chuckled the old man.  “A droll idea!  I’ll learn to play the flute!”

“Meet me at nine to-night at the Three Wise Men and—­good luck.  I’m off to the Sante.”