ossibly produce a sound
effect so oddly disturbing and strangely alien.

It was like no sound that Blake had ever heard before. Vibrant with
colossal power, it suggested a sustained note struck from a giant organ,
a note so low in pitch that it seemed a full octave below the lowest
bass note ever struck. Whatever it was, the thundering vibration of
infra-bass was coming nearer with startling swiftness.

* * * * *

It was impossible to locate the source of the mighty pulsing note. It
seemed to be coming simultaneously from all directions, like a great
hollow sphere of invisible sound waves closing in with the station
platform as its central focal point.

Helen's face was white with dread as she shrank closer into Blake's
embrace. Blake noted that the gangster across the platform was standing
tensely at bay with his back against the pillar and his right hand
thrust under his coat as he stared wildly about him in an effort to
discover the cause of the disturbance.

The rolling thunder closed in upon them with a final rush that brought
it so near that their very bodies seemed to vibrate in harmony with that
mighty note of shuddering bass. Then with startling abruptness the green
net came.

Out from the walls and down from the roof spurted scores of quivering
ribbons of blinding green flame. Swiftly the radiant tendrils rushed in
upon the shrinking three from every side, while the infra-bass thundered
in mighty crescendo.

Blake instinctively swept Helen close within the shelter of his arms in
an effort to protect her with his own body against the searing menace of
those onrushing green flames. The next moment the fiery ribbons were
upon them, lashing about their bodies, crossing and crisscrossing in the
air above and around them in a great tangled web of interlacing lines of
flame that filled the entire platform.

* * * * *

With a shock of relief Blake found that there was no heat in those
strange flames, but his relief was short-lived as the next second
brought him realization of the real menace of the radiant ribbons. There
was a solidity and strength in those glowing streamers that held them as
helplessly captive as though they were gripped in ribbons of steel.
Dazed and helpless, the three struggled for a moment in the meshes of
the weird net of flame like fish caught in the strands of some giant
cosmic seine.

The trembling thunder of infra-bas