Racing toward the south another flier sped toward Helium. In its
cabin a tall red man bent over the soft sole of an upturned sandal.
With delicate instruments he measured the faint imprint of a small
object which appeared there. Upon a pad beside him was the outline
of a key, and here he noted the results of his measurements.

A smile played upon his lips as he completed his task and turned
to one who waited at the opposite side of the table.

"The man is a genius," he remarked.

"Only a genius could have evolved such a lock as this is designed
to spring. Here, take the sketch, Larok, and give all thine own
genius full and unfettered freedom in reproducing it in metal."

The warrior-artificer bowed. "Man builds naught," he said, "that
man may not destroy." Then he left the cabin with the sketch.

As dawn broke upon the lofty towers which mark the twin cities
of Helium--the scarlet tower of one and the yellow tower of its
sister--a flier floated lazily out of the north.

Upon its bow was emblazoned the signia of a lesser noble of a
far city of the empire of Helium. Its leisurely approach and the
evident confidence with which it moved across the city aroused no
suspicion in the minds of the sleepy guard. Their round of duty
nearly done, they had little thought beyond the coming of those
who were to relieve them.