aid, then.

"But how?" demanded Welch. "The plants are well guarded. You know, of
course, that we are all on the lookout for something of the kind? We
thought we had provided against any sudden surprise. Where are we to look
for them?"

Then Ned pointed out the probable points of attack, and Welch sprang to
his feet in a fuming passion.

"The spillway and the locks," he cried. "And the point where the soft
earth extends under the dam! Come!"

"Bring four of your men who can be trusted," Ned advised, not leaving the
box.

"Yes, and what then?"

"Send a man to the light station and have tracers sent out, but instruct
him not to have the lights turned on until you give the signal."

"I understand," the foreman said. "We'll catch them with the goods!"

Four men, workmen, were strolling along the danger points within five
minutes, and another moved toward the electric switches which governed
that part of the illumination. Ned and Welch remained near the spillway.
The three boys, after whispered instructions from Ned, moved along the
line passing word from man to man.

It was a long and heart-breaking half hour, seemingly double that time,
that followed. The man from the switches came back and whispered to Welch,
and at that moment a shrill bird-call sounded in the darkness. This, in
turn, was followed by the report of a revolver, and then the light leaped
into the globes, making the place, the entire length of the canal dam, the
spillway and the locks, as bright as day.

There came a half-hearted explosion from the direction of the locks,
followed by more shots. Then everything was in confusion, and groups of
men gathered in four spots along the line. There were more shots and then
the three boys rushed, panting, to the position Ned and the foreman had
taken.

"They've got them!" Frank cried. "They've got every man of them--four Japs
with lighted fuses in their hands!"

"There must be more than four!" Welch cried.

"I think not," Ned replied. "This is hardly a job for many men to work on!
The four dare not take others into their confidence. Come! Suppose we
gather them in?"

"How do you boys know they've got them all?" demanded Welch. "The four men
must be some distance apart."

"Not too far for a revolver to carry a signal!" smiled Ned. "You probably
noticed four groups of shots? Well, the boys who have been acting as
messengers from man to man gave directions as to the number of shots for
each group!"