eering
eagerly at the negro.

By this time the negro was taking to the water, towing his miniature scow
and its explosive cargo as he swam.

"He must be a good swimmer, and also a good diver," concluded Tom. "With
my men patrolling the sea wall he must have to dive, some distance away,
swim under water, and remain there until he has secured one of the tubes
in place. Then he has to get back, out of range of the lanterns' rays, and
get his breath before he goes back to the next job. But maybe I can
interfere with his work to-night."

Though he rose and moved away, Reade, despite the darkness of the night,
was careful to keep himself concealed behind the bushes, so that he could
not be observed from beach or water. Shortly the young engineer was over
at the point in the jungle from which he had seen the negro emerge with
scow and explosives.

"The fellow must use a magneto, attached to wires running under the water,"
concluded Tom. "At that rate, the first real job is to find the magneto.
My, but Mr. Sambo Ebony may be wondering, to-night, why his blow-out
doesn't work as easily as usual!"

Simple as the search ought to have been, Tom Reade was soon on the point
of despair.

"If it isn't a magneto, or if I can't find it in time," Tom muttered
uneasily, "the mystery may remain nearly as great as ever, and the
explosion may be pulled off to-night, after all."

Twenty minutes passed before Reade, with all his senses alert, stumbled
on the concealed magneto. It had been so well hidden, under a mass of
rocks, that it would not have been astonishing had Tom missed it
altogether.

Attached to the magneto was the wire that must connect, in some way, with
the series of tubes that would soon be fastened in the retaining wall out
yonder. Yet this wire ran into the ground, and then vanished.

"Now, I've simply got to hustle!" sighed Tom Reade nervously. "If I don't
succeed in raising the wire, and in a mighty short space of time, I may be
to-night's fool yet. I'd really like to wish that on the black man, too!"

By using his eyes and his reasoning powers Reade, after twenty minutes more
of search, with some sly digging, unearthed a section of the wire some
dozen feet from the magneto.

"Now, it must be really the swiftest sort of work," murmured the young
engineer, after a glance seaward. He seated himself with his face turned
toward the Gulf, gathered the exposed section of wire up into his lap, then
drew a p