“Perfectly solid, you see,” he said to Hal.

“I see,” replied Hal.

Duval struck the open door several resounding blows.

“Also perfectly solid,” he remarked.  “If you had a gun now you might possibly blow the lock off, but, as you haven’t, you will be safe enough.”

He turned to his aide.

“You are sure he was not armed?”

“Sure.  I searched him carefully.”

“All right.  Then there is no need to search him again.”

With his revolver he covered the lad while he backed from the little room.

“Good-by,” he said, and jumping out quickly, slammed the door closed.

“Good-by,” Hal called after him, without a tremor.

“When the water begins to rise,” shouted Duval, through the door, “you may lose some of your nerve.  I’d like to stay and hear you cry for mercy, but I have other work to do.  However, my friend here will stay in the house, and I wouldn’t be surprised if he didn’t hear you upstairs.”

To this Hal made no reply.

He now turned his attention to an examination of the room in which he was confined.  The walls rose on all sides to a height of perhaps fifteen feet.  This he had perceived while the door stood open, but inside now it was perfectly dark, except for a tiny stream of light that filtered in from below the walls, which failed to reach the floor by less than an inch.

The lad felt the walls carefully with his hands.  They were perfectly smooth.  He placed his fingers on the floor.  It was dry.

He stood silent for some moments and then, becoming conscious of a strange sound, he again touched the floor with his fingers.  They came away wet.  Water was slowly trickling into the room.

The room was very small, and Hal realized that it would not take it long to fill.  Therefore he decided on instant action.

When Duval, before leaving the lad to his fate, had mentioned revolvers, Hal had feared for the moment that he might be searched anew; but, when Duval had said a second search was not necessary, the lad breathed easier.  His reference to blowing away the lock had not been lost on Hal, but the lad had already thought of that.

“Well,” he said to himself, “the sooner I act the better.  If Duval has left the house already I shall have but one to deal with.  If I wait until I am sure he has gone, I shall probably be drowned.  Here goes!”

Quickly he produced his pair of automatics, and, running his hand over the door, found the lock.  He placed the muzzle of one automatic right up against it, and holding the other in his other hand, ready for instant use should he encounter a foe on the opposite side, fired.

In the narrow room the shot sounded like an explosion of a cannon, and the force of it shook the lad from head to toe.  Smoke filled the little aperture, strangling him.  He pressed his weight against the door.  It did not yield.  Something had gone wrong.