set the groundcar's radio dial on the frequency
which had been agreed on for emergency Phoenix broadcasts during this
operation. If government monitors caught the broadcasts and jammed them,
there were alternate channels chosen. With only about two dozen radio
stations on all Mars, plus the official aircraft and groundcar band,
there was plenty of free room in the air.

There was nothing on the Phoenix frequency now but a little disconsolate
static.

The country through which he drove here was uninhabited lowland. The
human life on Mars, agricultural, industrial and commercial, was
concentrated under the domes of the cities. Except for a few tiny
individual domes at the edge of Mars City, there were no human
structures close to it except the airport and the spaceport, and these
were west and north of the city, respectively.

The highway struck straight and lonely through a faintly rippling sea of
gray-green canal sage, spotted occasionally with the tall trunk of a
canal cactus, rising above it. Later he would see infrequent dome farms,
but he could expect no more than two or three score of these in the
entire long drive to Hesperidum.

Dark slowed and entered the cloverleaf that took him onto the bypass
expressway. Even as he did so, the radio crackled and the thin voice of
the Chief sounded over the groundcar loudspeaker.

"Attention, Phoenix," said the Chief intensely. "Attention, Phoenix.
Emergency instructions. We have monitored reports that the government is
checking airlocks at all cities. Repeat: the government is checking
airlocks at all cities.

"Some Phoenix have been captured attempting to leave Mars City.
Instructions: those in Mars City do not attempt to leave but find
shelter with Phoenix friends. Those beyond dome without credentials, go
to assigned emergency rendezvous spots _outside_ dome cities. Repeat
instructions: those...."

Swearing under his breath, Dark pulled the groundcar to a stop beside
the highway. It was so simple! They should have foreseen that the
government would take such a step as soon as it was realized that the
Phoenix men were leaving Mars City. He himself evidently had gotten
through the airlock just in time.

But he had been assigned no outside rendezvous! Whether it was an
oversight or not, he did not know, but the only place he had been
instructed to go was Hesperidum. The only Phoenix contact he knew was
the South Ausonia Art Shop in Hesperidum; and now he could not e