“There is no planetary radiation that can be dangerous to a ship with Cosmic shielding. Weren’t we sent here to find out what has happened? What are we going to tell the Great Circle? It isn’t enough to establish a fact, we have to explain it-excuse me if this sounds like a lecture to schoolboys!” said Erg Noor and the usual metallic tones in his voice now had a note of ridicule in them. “I don’t imagine we can evade doing what is our plain duty.”

“The upper layers of the atmosphere have a normal temperature!” exclaimed Nisa, happily, on completion of her rapidly performed measurements.

Erg Noor smiled and began to put the ship down in a spiral each turn of which was slower than the last as they neared the surface of the planet. Zirda was somewhat smaller than Earth and no great speed was needed to circumnavigate it at low level. The astronomers and the geologist checked the maps of the planet with what was observed by Tantra’s optical instruments. There had been no noticeable change in the outlines of the continents and the seas gleamed calmly in the red sun. Nor had the chains of mountains changed the shapes that were known from former photographs — but the planet was silent.

The crew spent thirty-five hours at their instruments, relieving each other occasionally.

The composition of the atmosphere, the radiation of the red sun, everything agreed with formerly recorded Zirda data. Erg Noor looked for the Zirda stratosphere tables in his reference book. Ionization was higher than they showed. A vague and alarming concept was taking form in Noor’s mind.

On the sixth turn of the descending spiral the outlines of big cities became clearly visible. And still not a sound was recorded by the spaceship’s receivers.

Nisa Greet was relieved from her post for a meal and seemed to have dozed off for a while. She thought, however, that she had not slept for more than a few minutes.