The boys left the old tool house without spending any more time in conversation, and hastened down the ladders to the lower level. On the way down the last gangway they heard some one moving about in the darkness, and then came a cry of warning.
"Stand clear! Stand clear!"
"That's Ventner's voice!" exclaimed Will.
"There's a blast going off in a minute!" the voice came again.
"Now we've gone and done it!" exclaimed Will. "After all the trouble we've taken to make that fellow think we've left the country, we've let him bump right into us. I wonder if he really has fired the fuse?"
"Stand clear! Stand clear!" shouted the voice. Almost before the words had died out, the explosion came, tearing more than one pillar out of position and dropping a great mass of slate down on the floor of the cross-cutting.
For a moment the gases which filled the chambers were overpowering. The only wonder was that they were not ignited. The electric lights carried by the boys shone dimly through the smoke of the confined place.
"There goes Ventner," whispered Will, pointing to a figure moving swiftly through the half-light of the place.
"He's going to see what the shot brought down!" suggested Tommy.
The Boys rushed forward in a little group. When they gathered at the scene of the explosion, the detective was not there.