When the rolling thunder of infra-bass first came to their ears, Robert Blake and Helen Lawton were standing on the platform of a New York subway station waiting for the arrival of an uptown express to bear them to their homes.
They made a strikingly attractive couple as they stood there. New York had not had time as yet to remove the bronze tan of an outdoor life from Blake's ruggedly good-looking face. His tall athletic figure was still conspicuous for the lithe strength that had made him an All-Western tackle less than two years ago.
Standing beside Blake's husky figure, Helen Lawton looked like a tiny, very perfect, blonde doll, with an exquisitely molded face framed in curly bobbed hair that was the clear golden-amber hue of orange honey. There was a diamond sparkling on the ring finger of the girl's slim left hand, placed there by Blake.
It was well after midnight, and the only other passenger waiting on the station was a burly chap leaning against one of the white pillars on the other side of the platform. After a casual glance at the fellow, with his derby hat shoved far back from a low forehead, his blatantly conspicuous clothing, and the suspicious bulge under one arm-pit, Blake had mentally set him down as a minor gangster, probably a strong-arm man for some beer mob.
Blake and Helen had been standing there but a few minutes when the strange sound first became audible. For a moment Blake thought it was merely the rumbling roar of an express approaching far down the tunnel. Then he realized that no subway train could possibly 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....