t coast
of Florida, came into view. Dick shifted course a little. Three hours
more should see them over Abaco.

His flight had explicit instructions. As soon as the black gas had
rendered visible the headquarters of the Invisible Emperor, they were
to circle above, dropping their bombs. When these were exhausted, the
machine guns would come into play. There was to be no attention paid
to signals of surrender. They were to wipe out the headquarters, to
kill every living thing that showed itself--and the navy and the
marines would mop up anything left over.

The sun went down in a blaze of gold and crimson. Night fell. The moon
began to climb the east. The black sea, stretching beneath, was as
empty as on the day when it was created. Nothing in the shape of
navigation appeared.

Two hours, three hours, and old Evans turned round in his cockpit and
pointed. On the horizon a black thread was beginning to stretch
against the sky. It was Abaco Island, in the Bahama group. They were
nearly at their destination. An hour more--perhaps two hours, and the
deadly menace that threatened America might be removed forever. Dick
breathed a silent prayer for success.

* * * * *

They were over Abaco. A long, flat island, seventy miles or so in
extreme length, and fairly wide, covered with a dense growth of
tropical brush and forest, with here and there open spaces, near the
seacoast an occasional farm-house. Dick dropped to five thousand, to
three, to one. The moon made the whole land underneath as bright as
day.

There were no evidence of destruction by the hurricane. The farmhouses
stood substantial and well roofed. If death had struck Abaco Island,
it had been the work of man, not Nature.

Dick zoomed almost to his ceiling, until, in the brilliant moonlight,
he could see Abaco Island from side to side. For the most part it was
heavily wooded with mahogany and lignum vitae: toward the central
portion there was open land, but there was not the least sign of any
construction work.

Again he swooped, indicating to his flight to follow him. At a
thousand feet he examined the open district intently. Here, if
anywhere upon the island, the Invisible Emperor had his headquarters.
Was it conceivable that a gas factory, hangars, ammunition depots
could exist here invisibly, when he could look straight down upon the
ground?

Dick's heart sank. The hideous fear came to him that Graves had been
mistaken,