"Hist!" came from Billy's lips, and they halted.
"There it is," he said in a low tone.
They clustered about him as he pointed to the left. There, sure enough, was the electric bulb glowing, and behind it the outline of a door. Turning into the passage and inwardly thankful that as yet no rats had been encountered, they made their way toward the light.
The door, as revealed by the light, was of heavy oak. There was no crack or crevice in it anywhere. Standing close to the door they listened intently for any sound from the other side. Everything was absolutely quiet. All that they could hear was their own excited breathing.
Frank put his hand on the knob of the door and flashed a look of mute inquiry at his comrades. They nodded understandingly, and inch by inch Frank noiselessly drew the door open.
There was no light in the room beyond, but a ray from the electric bulb outside fell on a row of bottles and retorts that indicated a chemical laboratory.
Frank had drawn his flashlight from his section pocket and was about to turn it upon the room, when suddenly the room became radiant with a perfect flood of light. At the same time there was the sound of a quick step in the hall beyond the room, the click of a door knob, and Frank had just time to push the heavy oaken door nearly to, when the further door opened and a man came into the room.
Through the crack of the door Frank caught a glimpse of the man's face and started back in surprise.