from the hillock, up the wind to where at the edge of the
forest they stood gazing.

The blue fire had spread over a distance of several feet. A sluggish,
boiling, bubbling area of flame. Tongues now the height of a man. And
from them, rolling upward, a heavy black cloud--deadly fumes thick,
blacker than the night, spreading out, welling forward over the forest
toward the Great City slumbering in its falsely peaceful security.

At last Elza knew. Stood there, cold, shuddering, thinking with all the
power of her mind and being:

_"Death, Jac! Death to all the City! The black cloud of death!"_

Oblivious to Tarrano she stood until at last the rocky eminence was one
great mass of the surging blue fire. And the black cloud, compact as a
thunder-head, rolled onward.

_"You can see it coming! Death Jac! Death to all the City!"_

A sudden madness descended upon Elza. She felt abruptly that her warning
was futile, felt an overpowering desire to run. Run somewhere--anywhere,
away from the lurid sight she was facing. Or run perhaps, to the Great
City; to race with that black cloud of death; to run fast and far, and
burst into our palace to warn us.

Tarrano himself lost in triumphant contemplation of what he had done,
for the moment was heedless of Elza's presence. With white face upon
which the blue glare had settled like a mask of death, Elza turned
silently from him. Forgetful of that horrible thing they had
encountered--others of its kind which might be lurking about--she turned
silently and plunged into the black depths of the forest.

CHAPTER XXIX

_A Woman's Scream_

"The black Cloud of Death!"

We stood there at the casement of the palace, gazing with a growing
terror at the visible evidence of the tragedy which threatened. A black
cloud off there in the distance, spreading out, rolling inexorably
toward us. And then came the wind, and with it a breath of the black
monster--a choking, horrible suggestion of the death rolling already
over the city.

We must have been fascinated at the casement for some considerable time.
Elza's thought messages had ceased. Abruptly I came to myself.

"The Black Cloud of Death!" I turned to Georg and Maida. "Alarm the
city! Arouse them all! Alarm--"

Maida's face was white: she flung off Georg's arm which had been
protectingly around her. "The siren--"

Terrible moments, those that followed. Confusion; panic; death!

The public siren in the tower by the lagoon e