The Zeppelin forced to travel low.]

If there was no disturbance in the clouds themselves there was among
them something very active, something that drilled its way through them
with a muffled whirring, something that was oblong and lean and light of
texture, that was ominous and menacing for all its buoyancy. The sound
it made was too high up, too thickly shrouded by clouds, to determine
its precise position. It gave forth a breathing of persistent, definite
rhythm. This was plainly not the wing-stroke of a nocturnal bird; for no
bird, big or little, could advertise its flight in such perfect
pulsation. And yet it was a bird, a Gargantuan, man-made bird with
murder in its talons and hatred in its heart. From its steel nest in
Germanized Belgium this whirring monster had soared eight thousand feet
and crossed the Channel with little fear of discovery. It had penetrated
the English Coast somewhere down Sheerness way and over Southend and
then, dropping lower, had sought and found through the haze the tiny
train whose locomotive had just fluted its brief salutation to
Walthamstow. To the close-cropped men on the Zeppelin, the string of
cars far down under their feet, with its side-flare from lighted
windows, its engine's headlamp and its sparks, had proved a providential
pilotage. They knew that this train was on the main line, and that it
would lead them straight to the great Liverpool Street Station, and that
was London, and it was London wharfs and ammunition works along the
Thames that they had planned to obliterate with their cylinders of
mechanical doom. But the moist clouds which aided so materially in
hiding the Zeppelin's presence from below also worked for its defeat, in
so far as its ultimate objective was concerned, for to keep the guiding
train in view it was compelled to travel lower and yet lower--so low,
indeed, as to make it a target for Kitchener's sentinels.

[Sidenote: The switchman signals "danger."]

[Sidenote: The train stops at Walthamstow.]

Somehow, by sight or intuition or the instant commingling of the two,
old Tom Cumbers became aware of the danger above him; for he sprang to
his switch, shut off all the cheery blue and white lights along "the
line" and swung on with a mighty jerk the ruby signal of danger. The
engineer in the on-rushing train jammed down his brakes and brought up
his locomotive with a complaining, grinding moan, a hundred yards beyond
Walthamstow station. Tom Cumbers had