r to the gang of Ganymedans holding the
stone nozzle and looking expectantly up at the large, round hole in
the cloud ceiling.

Nona stood close to Grant. "What are they doing with the queer
affair?" She indicated the nozzle.

"I'm afraid we'll find out only too soon," he answered grimly.
"Look--" he broke off.

Far overhead, through the great round orifice, darted a tremendous
shape, pointed, glittering.

"Why, that's the _Althea_," Nona exclaimed.

"Yes. Now watch. Damn--all we can do is watch," Grant gritted between
his teeth.

* * * * *

Down sped the gleaming liner, pride of the fleet. The men at the
mirror were swerving it on gimbals until a ray from it flashed on the
burnished nose. As though it were a physical impact, the vessel
slackened its tremendous speed and hung suspended midway between the
cloud concavity and the island.

The men with the nozzle spurred into activity. A thin stream of fluid
shot out of the orifice straight up for the captive liner. The tip of
the expanding spray impinged on the hull--and Nona gasped her
astonishment. For the liquid passed clean through the hull as though
it were a porous network instead of four-inch thick beryllium-steel.

"Just as I thought," Grant groaned. "Lethal gas that penetrates
everything. Those poor people on board--for their own sakes I hope
none remained alive to hit this."

"Can't we do anything?" Nona asked desperately.

"Nothing for the _Althea_. But plenty to prevent any more disasters
like it." There was a hard ring to his voice. "Come on." He stepped
off the transparent slab onto the stone floor of the island.

"Where to?" asked Nona, following.

"We're going to locate that orange oval we saw from the _Althea_.
That's the secret of all this. The pool of liquid fire here is
unimportant, secondary."

They were at one edge of the floating island. The other side was
hidden from them by the solid wall that stretched across its full
diameter.

"We'll scout beyond there," Grant pointed out. "I'll miss my guess if
what we're looking for is not on the other side."

As they started for the wall, they saw the Althea brought slowly down
to the rock, another captive to swell the motionless fleet. It did
not take them long to reach the barrier. Some fifty feet high it was,
of smooth polished Ganymedan stone, and no door or opening in its
straight unbroken surface.

"How shall we get through?" Nona asked.

Grant s