He noticed that the air was not good, and this soon gave him cause for additional alarm.  If he could not get any fresh air, he might smother before anybody came to release him.

Once more he went over the walls and the flooring, and even pounded on the iron door.  It was all to no purpose.  He was as close a prisoner as if encased in a stone tomb.

“Perhaps they will leave me here until I either smother or starve to death,” he reasoned.  “It would be an easy way of disposing of me.  And Miss Langmore and Mr. Case would wonder how I came to disappear so mysteriously.”

He set the boxes on the floor, and, standing on one of them, proceeded to examine the roofing of the vault more carefully.  He found one of the iron arches a bit loose at one end, and pulled upon it with all his might.

The result was greater than he had anticipated.  The iron brace came down, and with it fell several dozens of brick, some hitting the detective on the legs and feet.  He shrank back against the shelves, and so avoided getting the shower on his head.  The lantern was smashed, leaving him in total darkness.

As soon as the fall was over, he pulled the boxes from beneath the bricks and piled them one on top of the other.  Mounting as high as he could, he felt around, secured a hold on some bricks and stones above, and hauled himself upward.

“Now to get out somehow!” he told himself.  “No more lingering in this den of criminals!”

He felt around, as he moved forward.  On all sides the walls were wet and slimy.  He advanced with care, resolved to avoid all pitfalls, were it possible to do so.  He was in a place where the roofing was no higher than his shoulders, so he had to stoop as he progressed.

A moment later he found himself in a narrow passageway, with rocks on one side and a heavy wooden partition on the other.  Through a slit in the partition a faint light was streaming.

Adam Adams tiptoed his way to the slit and looked through.  Beyond he made out the printing room of the counterfeiting plant.  Only one man was present, the big-boned fellow known as Number Four.  He was seated on the corner of a rude table, idly tearing some paper into strips, and evidently thinking deeply.

As the detective was about to move on, another person entered the printing room.

“Did they get him?” asked Number Four eagerly.

“Yes,” was the short reply.

“Where was he?”

“You’d never guess.”

“At the river?”

“No; in the vault.”

“What!  How did he get there?”

“Nobody knows.  He must have found the door open.  But it’s against the rules for anybody to leave that door unlocked.”

“I know that,” said Number Four, and heaved a deep sigh.

“Say, you don’t like your job, do you?” went on the other counterfeiter, with a sniff.

“Would you like it?” demanded Number Four, half angrily.