Greg had reached the boundary of the Western Central freight yards and had turned east to find a better street down-town when he was startled by a violent rapping on the glass behind him. At the same moment de Socotra opened the cab door. "Go back! Go back!" he cried in a strained, harsh voice. "Back to the apartment!" As he turned around in the street, Greg stole a glance into the back of the cab. He could not see the face of either man, but revealed by the light of a street lamp he saw the little black book open in de Socotra's hands. So the worst had happened. Saunders had betrayed them, and de Socotra had discovered the substitution. Greg's heart contracted sharply. How could he warn Amy in time? He turned back into Amsterdam Avenue, and headed north again. In his efforts to collect his thoughts he instinctively slowed down. De Socotra hammered on the glass and yelled: "Faster! Faster! What's the matter with you?" Presently he changed his mind. Opening the door again he said: "Stop at that drug-store yonder, I want to telephone." The two men tumbled out of the cab. They were disputing excitedly in Spanish. Saunders seemed to be making some kind of appeal, which de Socotra furiously denied. The latter's face was livid and distorted with rage. Gone was the smiling courteous veneer. Greg was appalled at the revelation of the man's true character. On the other hand Saunders seemed almost ready to weep. "He is scared now at what he started," thought Greg grimly. De Socotra, waving Saunders away, went into the drug-store. Saunders, holding his hands above his head and talking to himself, walked blindly away down the side street. "He hasn't even got wit enough to warn her what is coming," thought Greg. "I must do it." Through the lighted windows of the drug-store Greg saw that the telephone booth that de Socotra entered adjoined the soda-water counter. Obeying a sudden impulse he followed him into the store. The soda-clerk grinned at Greg and cocked a humorous eyebrow in the direction of the telephone booth. "Bug-house, I guess?" Greg shrugged and grinned in kind, and ordered a lemon phosphate. While it was being drawn he edged along the counter towards the booth. Through the glass he saw that de Socotra had his back towards the door--for that matter Greg didn't much care now if he did begin to suspect him. Many of these supposedly sound-proof booths are flimsy affairs, and Greg, straining his ears, was able to hear a good deal of what de Socotra was saying. The soda-clerk, taking in the situation, continued to grin appreciatively. De Socotra got the number he asked for and started talking. The first thing Greg heard distinctly was: "Yes, treachery in my own household! But I'll take care of that."