“I’ll just step over and see how Joe is,” thought Blake.  He judged it lacked half an hour yet of midnight.

He found Joe busy mending a broken wire that ran from the battery to the flashlight powder chamber.

“Just discovered it,” Joe whispered.  “Lucky I did, too, or it would have failed me just when I needed it.”

“Is it fixed?” asked Blake, as his chum straightened up in the darkness.

“Yes, it’ll do for a while, though it’s only twisted together.  Say, but isn’t it dark?”

“It sure is,” agreed Blake.

Together they stood there near the great dam.  There came to their ears the splashing of water over the spillway, for the lake was high, and much was running to waste.

“Well, I guess I’ll be getting back,” said Blake in a low voice.  “No telling when things will happen now.”

As he started to go away Joe remarked: 

“Where are you wearing your watch?  I can hear it over here.”

“Watch!  I haven’t mine on,” Blake answered.  “You can’t see it in the dark, so I left it on the boat.”

“Well, something is ticking pretty loud, and it isn’t mine,” Joe said, “for I did the same as you, and left it in my cabin.  But don’t you hear that noise?”

They both listened.  Clearly to them, through the silence of the night, came a steady and monotonous tick—­tick-tick—­

“It’s the clockwork of the automatic camera,” Blake whispered.

“It can’t be,” answered Joe.  “That’s too far off.  Besides, it’s a different sound.”

They both listened intently.

“Tick!  Tick!  Tick!” came to them through the dark silence.

CHAPTER XXV

MR. ALCANDO DISAPPEARS

For several seconds Blake and Joe stood there—­without moving—­only listening.  And that strange noise they heard kept up its monotonous note.

“Hear it!” whispered Joe.

“Yes,” answered Blake.  “The brass box—­the box—­he had!”

“Yes,” whispered Joe.  All the suspicions he had had—­all those he had laughed at Blake for harboring, came back to him in a rush.  The brass-bound box contained clockwork.  Was it an alarm after all?  Certainly it had given an alarm now—­a most portentous alarm!

“We’ve got to find it!” said Blake.

“Sure,” Joe assented.  “It may go off any minute now.  We’ve got to find it.  Seems to be near here.”

They began looking about on the ground, as though they could see anything in that blackness.  But they were trying to trace it by the sound of the ticks.  And it is no easy matter, if you have ever tried to locate the clock in a dark room.

“We ought to give the alarm,” said Blake.

“Before it is too late,” assented Joe.  “Where can it be?  It seems near here, and yet we can’t locate it.”

“Get down on your hands and knees and crawl around,” advised Blake.  In this fashion they searched for the elusive tick-tick.  They could hear it, now plainly, and now faintly, but they never lost it altogether.  And each of them recognized the peculiar clicking sound as the same they had heard coming from the brass-bound box Mr. Alcando had said was his new alarm clock.