“There’s no number,” he called out.  “Just keep going.”

The driver grumbled and cracked his whip, and a moment later, peering back through the front window, he saw his eccentric fare absorbed in examining a white leather bag.  He could see him distinctly by the yellow light of his two side lanterns.  The young man had opened one of the inner pockets of the bag, drawing out a flap of leather under which a name was stamped quite visibly in gilt letters.  Presently he took out a pocket knife and tried to scrape off the name, but the letters were deeply marked and could not be removed so easily.  After a moment’s hesitation the young man carefully drew his blade across the base of the flap, severing it from the bag, which he then threw back on the seat, holding the flap in apparent perplexity.

All this the driver observed with increasing interest until presently Kittredge looked up and caught his eye.

“You’ve got a nerve,” the young man muttered.  “I’ll fix you.”  And, drawing the two black curtains, he shut off the driver’s view.

As they neared the end of the Rue de Vaugirard, the American opened the door again and told the man to turn and drive back, he wanted to have a look at Notre-Dame, three full miles away.  The driver swore softly, but obeyed, and back they went, passing another cab just behind them which also turned immediately and followed, as Kittredge noticed with a gloomy smile.

On the way to Notre-Dame, Kittredge changed their direction half a dozen times, acting on accountable impulses, going by zigzags through narrow, dark streets, instead of by the straight and natural way, so that it was after midnight when they entered the Rue du Cloitre Notre-Dame, which runs just beside the cathedral, and drew up at a house indicated by the American.  The other cab drew up behind them.

“Tell your friend back there,” remarked Kittredge to his driver as he got out, “that I have important business here.  There’ll be plenty of time for him to get a drink.”  Then, with a nervous tug at the bell, he disappeared in the house, leaving the cloak and bag in the cab.

And now two important things happened, one of them unexpected.  The expected thing was that M. Gibelin came forward immediately from the second cab followed by Papa Tignol and a policeman.  The shadowing detective was in a vile humor which was not improved when he got the message left by the flippant American.

“Time for a drink!  Infernal impudence!  We’ll teach him manners at the depot!  This farce is over,” he flung out.  “See where he went, ask the concierge,” he said to Tignol.  And to the policeman:  “Watch the courtyard.  If he isn’t down in ten minutes we’ll go up.”

Then, as his men obeyed, Gibelin turned to Kittredge’s driver.  “Here’s your fare.  You can go.  I’m from headquarters.  I have a warrant for this man’s arrest.”  And he showed his credentials.  “I’ll take the things he has left.”