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!"