Bob stared at the windows. The head and shoulders of the unknown had disappeared and the distant noises of the street were clearer now, drifting in through the broken window. Merritt Hughes should arrive at almost any minute and Bob felt that the wise and sensible thing now was to play as safe as possible and await the arrival of help. Crouched down between the desks, he was in a position to watch the file with the radio documents and he knew that if they were molested he would fight with all his strength to protect them. As the seconds passed into minutes Bob felt his muscles tensing and his nerves becoming tighter. There was no sound in the room; there had been no sound since the echoes of the shot had died away. Had his missile disabled the other man; had the shot been fired involuntarily? They were questions he couldn’t answer. Why didn’t a night guard appear in the corridor outside? Bob believed that he would have risked a call for help if anyone passed. But strain as he might, he could hear no one outside the door. Then Bob broke into a cold sweat. The man who had fired the shot was almost beside him. Bob had been so intent upon listening for some sound in the corridor that he had failed to hear the unknown crawling toward his own hiding place. Bob sensed, rather than saw, what was happening. He could hear the steady breathing of the other and he held his own breath. Would the man crawl on down the room toward the doorway or would he turn in between the desks where Bob had sought shelter? The dark blob that was the other’s head and shoulders appeared between the desks and Bob waited for an agonizing interval. Then the figure moved on and Bob could breathe once more. That had been a close call. Then came another sound that brought Bob back to the alert. There was the faint shrilling of a siren. Was it a fire alarm? Bob listened intently. No, it was sharper, more penetrating. A police car. That was it! It was evident that the other man had also heard the night alarm for Bob heard a muffled exclamation. He doubted if it was an alarm turned in by his uncle for his protection, but at least it was enough to alarm the marauder and Bob’s muscles snapped back to steelly tension. He had gone so far now that he had no intention of allowing the other to escape at the last minute. The steady wail of the siren drew nearer as down on the avenue the speeding machine dashed through traffic lights and skidded past other machines which were pulling over to give it the right of way. The siren rose to a crescendo and then died to a wail as the police car swayed to a stop somewhere below and Bob knew then that rescue was near. His uncle, feeling the need for quick re-enforcements, had evidently called on the Washington police and commandeered a cruising radio car. From somewhere out of the darkness came a low, deadly voice.