d them that he was tightly
bound.

Then they were at the door, which, shivering and bending from the
battering without, showed signs of giving in. With herculean efforts
they dragged a heavy divan over and wedged it tightly against it; then
added other furniture in a tight supporting pile. But the door, of
some light metal, was not built to stand such a siege, and was
buckling further inward with each blow being dealt it. More and more
plainly the two men could hear the triumphant snarls and howls of the
animal-men.

Frantically they ransacked the rooms looking for what they thought
might be weapons, but found none. They looked at each other with
dismay. It was only a question of time--minutes--before the slaves
would break in. What could they do?

* * * * *

In that tense moment of indecision a low, weak voice reached their
ears--a woman's voice, and one they remembered well.

"Vivian!" cried Clee, and ran to the alcove, from whence it had seemed
to come. The girl's next words brought them understanding.

"Clee--Jim--it's Xantra! He's willing the slaves to break in! He's
lying bound on the floor, but he's conscious!"

Clee ran to where he had left the invisible man, cursing himself under
his breath for being an utter ass for not having guessed this. His
groping fingers quickly found the squirming Xantra's neck; and he had
begun to throttle him into unconsciousness when Vivian called out:

"No! Don't! That won't stop the slaves: they've already been given the
order! We've got to make Xantra stop them! Here--drag him to the
work-table! I've got something--"

Wondering what the girl was about, Clee relaxed his grip on the
invisible man's neck and complied. But he suddenly understood--and
Jim, too--when he saw coming through the air the pair of
thought-sending helmets. He had a way of communicating with Xantra, of
course! He saw the larger helmet lower to rest over the head he was
still holding; then soft hands placed the other over his own.

As it settled down a great crash sounded in the other room: the door
had given in. It was still held almost in place by the tightly-wedged
furniture, but that would not hold the animal-men long.

"Hurry!" cried Jim. "I'll stand by the door!" And he was already on
his way to it.

Clee saw the small panel on the table above; saw the knob on it turn.
He caught Vivian's excited voice. "Tell him to order them to stop,"
she said; "or else--or e