lay on the stocks.

By this time a noise that plainly proceeded from the use of tools
came to the ears of the boys. Their nerves were on the keenest tension
as they reached the stern of the propped-up hull.

Then they came in sight of the quarry. Almost in the same flash they
realized what the night's mischief was.

Depending wholly on the light of a dark lantern that lay on the floor
of the shed, Owen, with two or three tools, was swiftly, wickedly
tampering with one of the sea-valves belonging to one of the forward
water compartments of the submarine.

This valve, if leaking badly when the craft lay submerged, would let
in enough water to cause the "Pollard" to lurch and then go, nose-first,
to the bottom. It was wholly possible, too, that a capable workman
could tamper with the valve so that, on casual inspection, the damage
would not be detected.

Hal Hastings's heart beat fast as he viewed this dimly illumined piece
of cowardly treachery. His fingers itched to lay hold of Josh Owen,
uneven though the fight might be with both boys for assailants.

But Jack Benson, though his first impulse was to let out a Comanche
yell, and then dart forward into the fray, instantly conceived a plan
that he thought would work better.

Gripping his chum's arm for silence, Jack whispered in his ear:

"Can you set the camera for universal focus, here in the shadow?"

"I--I think so," came Hal's low, quivering reply.

"Do it--like lightning, then!"

In his hand Jack held the flashlight "gun." It was one of those patent
affairs, arranged to fire a charge of magnesium powder by the explosion
of a cap when the trigger was pressed.

Dropping to one knee, Hal set the camera, half by instinct, half by
guess. While he did so, Jack fixed a charge of the powder in the
firing pan of the "gun."

These preparations made hardly any noise; such as might have been
heard in a silent room was drowned by the tap-tap of a small hammer
that Josh Owen was at the moment using.

And now, without glancing back at the stern, the ex-foreman half-turned
his head, so as to give a profile view of his face.

Hal, kneeling, turned up quickly to nod the signal that the camera
was ready.

Pop! Flare!

As the cap exploded, a blinding flash filled that side of the shed
for a brief instant. It was as through a lightning bolt had plunged
into the place.

Wholly unprepared for any such happening, Josh Owen let out a yell
of fear, rose up and