around a corner, took
careful aim at the foremost attacker. At the first whispering impact
of the beam the Martian sprawled, dead.

The soldiers were caught at a disadvantage. They were expecting club
or fist, but not the neuro-beam. Nevertheless Sime had no more easy
opportunities. The Martians flung themselves down behind the bulge of
the curved stairway, and the air became acrid under the malignant
neuro-beams.

None of them reached Sime directly, but the stone walls reflected them
to some extent, and even under their greatly weakened power he become
cold and sick.

The situation was by no means to his liking. There were other weapons
to be reckoned with, and he tried to keep consciousness from slipping
away from him. When at last his breathing became easier and his
diaphragm moved without pain, Sime knew that danger was greatest. For
this relief meant that the Martians had withdrawn down the stairway.

"Good-by, boys!" he thought, as he sprinted up into the comparative
safety of the open. He motioned to Tolto, who stood hopefully waiting
with his great war club, to stand clear.

* * * * *

There it was! Sime saw the faint phosphorescent reflection against the
stone where the stairway curved. He did not wait to see the tiny
pellet of the atomic bomb floating up, but threw himself flat on the
roof, tugging at Tolto, who understood and followed suit.

Even lying prone, and below the edge of the explosion cone, they were
nearly blown off the roof. Though no larger than a pinhead, the bomb
had the power of a thousand times its weight in fulminate of mercury.
When the rain of small stones and dust had subsided, they rubbed their
eyes and saw that the airlock was no more. In its place was a shallow
pit, ending with the top of the battered stairway.

"Down after 'em!" Sime husked out of a raw throat. "Before they think
it's safe to come after us!"

He led the way, the giant after him, carrying his club and a huge rock
fragment. Sime saw a cautious peering head, and that Martian died
instantly. Then they were around the bend and in the middle of a
fight. Sime deflected a hand that held a pistol, and its beam killed
another Martian who was about to let Tolto have it at close range.

There was a light-wand affixed to the wall a trifle further down.
Tolto waded through the ruck of smaller men, tore it from its socket
and hurled it up the stairs. A short sword bit into Sime's shoulder,