scended to the trap-door.

It must be nearly twelve, Kendrick knew. He couldn't look at his
watch, for it as well as himself was invisible. Indeed, even as they
stood there, poised for the plunge, a faint whistle rose from below.

Marjorie trembled.

"Steady!" he spoke. "Some of them always blow a minute or two before.
Are you ready?"

"Yes!"

"Then press your button--jump!"

Even as they leapt, the sickening thought came that perhaps the
escalator ray was no longer running. But the fear was unwarranted.
They were caught up, whirled gently downward.

Moving along laterally, as they descended, they were able to land
without difficulty in the middle of a deserted street near the
Consolidated Electric laboratory.

"Thank heaven!" she sighed, as their feet touched solid ground. They
pressed off both buttons, becoming visible once more.

"Echo!" he agreed. "So let's--"

* * * * *

But Kendrick never completed that sentence--for now whistles all over
the metropolitan area, rising from the generating plants, announced
the ominous hour.

It was high noon. The ultimatum had expired.

Lifting tense faces to the disc, they waited. Would that stupendous
ray be hurled back upon itself? Or would it sear through their
makeshift defense, plunging them and the whole great metropolis into
oblivion?

Suddenly, cataclysmically, the answer came.

There burst a withering whirlwind from the disc. It struck that mighty
concave cathode of interlaced waves above the city. There followed an
instant's clash of titanic forces. Then the cathode triumphed, hurled
it back.

Rocked by a concussion as of two worlds in impact, blinded by a glare
that made the sunlight seem feeble in comparison. Marjorie and
Kendrick clung together, while the disc grew into a satellite of
calcium fire in the sky.

Presently, as the conflagration waned, they opened their eyes.
Gravely, but with deep thanksgiving, they searched each other's faces.
In them they read deep understanding, too, and a new hope.

"I think we'd better go and find father," she said at length, quietly.

"I think so too!" he agreed.

As they headed toward the laboratory, a fine, powdery dust, like
volcanic ash was falling.

It continued to fall until the city streets were covered to a depth of
an inch or more.

Thus passed the menace of Vada.

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