As I climbed carefully to a lower branch so as not to reveal my presence by the shaking of the foliage, I heard a low whistle. It was Rojas.

"Who whistled?" demanded a voice somewhere in the courtyard. There was no reply.

Rojas could not have come at a worse time; I did not answer her; I did not know what to do, but Ptor Fak evidently thought that he did, for he answered the whistle. He must have thought that it was I who was signalling to him.

"They're on the roof!" cried a voice. "Quick! up that tree!"

Now the only tree that overhung the roof was the one that I was in, and if I remained there I was sure to be discovered. There was only one thing for me to do and that was to go up on the roof myself, and I did so as quickly as I could.

I hadn't taken half a dozen steps after I arrived, before I bumped into someone.

"Zodanga?" I whispered. I didn't wish to speak Ptor Fak's name, but I knew that he would understand if I spoke the name of the country from which he came.

"Yes," he replied.

"Find the flier and stay near it until I come." He pressed my arm to show that he understood, and was gone.

I could see the tree up which I had come shaking violently; so I knew that a number of warriors were climbing up in pursuit of me, though how in the world they expected to find me, I don't know.

It was a most amazing situation; there must have been at least a dozen men on the roof and possibly still others down in the courtyard where I knew Rojas to be, yet both the roof and the courtyard were apparently deserted—neither the eye nor the ear could perceive any living thing; only when someone spoke was the illusion dispelled, and presently I heard a voice a short distance away. "He has probably gone this way— the city wall lies nearest in this direction. Spread out and comb the roof right to the city wall."

"It's a waste of time," said another voice. "If someone has given him the secret of invisibility, we can never find him."

"I do not think it was he, anyway," said a third voice; "there is no way in which he could have become invisible—it was unquestionably the ghost of Motus that spoke."