In the tower, Gordon led the way up to the glass-walled laboratory where rested the strange instruments of mental science that had been devised by the real Zarth Arn and old Vel Quen.

Gordon went over in his mind what the old scientist had told him about the operation of the telepathic amplifier and the mind-transmitter. He checked the instruments as carefully as he could.

Hull Burrel watched wonderingly, worriedly. Finally, Gordon turned to him.

“Hull, I'll need your help later. I want you to do as I ask even if you don't understand. Will you?”

“You know I'll obey any order you give,” burst the big Antarian. “But I can't help feeling worried.”

“There's no cause to-in a few hours you'll be on your way to Throon again and I'll be with you,” Gordon said. “Now wait.”

He put the headpiece of the telepathic amplifier on his head. He made sure it was tuned again to Zarth Arn's individual mental frequency as Vel Quen had instructed. Then he turned on the apparatus.

Gordon thought. He concentrated his mind to hurl a thought-message amplified by the apparatus, back across the abyss of dimensional time to the one mind to which it was tuned.

“Zarth Arn! Zarth Am. Can you hear me?”

No answering thought came into his, mind. Again and again he repeated the thought-call, but without response.

Wonder and worry began to grip Gordon. He tried again an hour later, but with no more success. Hull Burrel watched puzzledly.

Then, after four hours had passed, he desperately made still another attempt.

“Zarth Arn, can, you hear me? It is John Gordon calling.”

And this time, faint and far across the unimaginable abysses of time, a thin thought-answer came into his mind.

“John Gordon! Good God, for days I've been waiting and wondering what was wrong. Why is it that you yourself are calling instead of Vel Quen?”

“Vel Quen is dead!” Gordon answered in swift thought. “He was killed by League soldiers soon after I came across to this time.”

He explained hurriedly. “There has been galactic war here between the Cloud and the Empire, Zarth. I was swept into it, couldn't get back to Earth to call you for the exchange. I had to assume your identity, to tell no one as I promised. One man did learn of my imposture but he's dead and no one else here knows.”

“Gordon!” Zarth Arn's thought was feverish with excitement. “You've been true to your pledge, then? You could have stayed there in my body and position, but didn't.”

His excited thought raced on. “I've had my troubles here on your ancient Earth, They had me in a hospital for a while for amnesia because I couldn't remember your past.”

Gordon told him, “Zarth, I think I can arrange the operation of the mind-transmitter to re-exchange our bodies, from what Vel Quen explained to me. Tell me if this is the way.”

He ran over the details of the mind-transmitter operation in his thoughts. Zarth Arn's thought answered quickly, corroborating most of it, correcting him at places.

“That will do it-I'm ready for the exchange,” Zarth Arn told him finally. “But who will operate the transmitter for you if Vel Quen is dead?”

“I have a friend here, Hull Burrel,” answered Gordon. “He does not know the nature of what we are doing, but I can instruct him how to turn on the transmitter.”

He ceased concentrating, and turned to the worried Antarian who had stood watching him.

“Hull, it is now that I need your help,” Gordon said. He showed the switches of the mind-transmitter. “When I give the signal, you must close these switches in the following order.”

Hull Burrel listened closely, then nodded understandingly. “I can do that. But what's it going to do to you?”

“I can't tell you that, Hull. But it's not going to harm me. I promise you that.”

He wrung the Antarian's hand in a hard grip. Then he readjusted the headpiece and again sent his thought across the abyss.

“Ready, Zarth? If you are, I'll give Hull the signal.”

“I am ready,” came Zarth Arn's answer. “And Gordon, before we say farewell-my thanks for all you have done for me, for your loyalty to me.”

Gordon raised his hand in the signal. He heard Hull closing the switches. The transmitter hummed, and Gordon felt his mind hurled into bellowing blackness…

Chapter XXVIII. Star-Rover's Return

GORDON awoke slowly. His head was aching, and he had an unnerving feeling of strangeness. He stirred, and then opened his eyes.

He was lying in a familiar room, a familiar bed. This was his little New York apartment, a dark room that now seemed small and crowded.

Shakily, he snapped on a lamp and stumbled out of bed. He faced the tall mirror across the room.

He was John Gordon again. John Gordon's strong, stocky figure and tanned face looked back at him instead of the aquiline features and tall form of Zarth Arn.

Gordon felt a sudden dazing wonder that shook him to the depths of his being.

“Was it all a dream? Could it all have been only dream born in my mind?”

He shook that thought from him. He knew better. Strange and eerie as it all had been, it was no dream.

He stumbled to the window and looked out on the starlit buildings and blinking lights of New York. How small, cramped, ancient, the city looked now, when his mind was still full of the mighty splendors of Throon.

Tears blurred his eyes as he looked up at the starry sky. Orion Nebula was but a misty star pendant from that constellation-giant's belt. Ursa Minor reared toward the pole. Low above the roof-tops blinked the white eye of Deneb.

He could not even see Canopus, down below the horizon. But his thoughts flashed out to it, across the abysses of space and time to the fairy towers of Throon.

“Lianna! Lianna!” he whispered, tears running down his face.

Slowly, as the night hours passed, Gordon nerved himself for the ordeal that the rest of his life must be.

Irrevocable abysses of time and space separated him forever from the one woman he had ever loved. He could not forget, he would never forget. But he must live his life as it remained to him.

He went the next morning to the big insurance company that employed him. He remembered, as he entered, that he had last left it weeks before, afire with the thrill of possible adventure.

The manager who was Gordon's superior met him with surprise on his face.

“Gordon, you feel well enough now to come back to work? I'm glad.”

Gordon had to speak carefully. He still did not know all that had happened to Zarth Arn in his body, during these weeks.

“Yes, I think I'd like to get back to work,” he said slowly.

“Doctor Willis will have to okay you first, of course,” said the other. “But he said when you left the hospital that it shouldn't take too long for you to recover completely.”

Gordon remembered Willis, the company's head physician, who rose with a welcoming smile on his face when he entered.

“Gordon, how are you feeling? Has your amnesia all left you?”

Gordon nodded. “It has. I can remember my past perfectly now.”

He gathered quickly that Zarth Arn's ignorance of this world and time had caused him to be placed in a mental hospital for a short time, and that Willis had treated him there for amnesia.

“I'm mighty glad,” Willis was saying. “I was afraid for a time that you'd end up like that woman in the hospital-room next to yours-you remember, the woman named Ruth Allen who'd lost her mind from shock and lay in permanent coma.”

“I'm all right now, doctor,” Gordon repeated steadily. “And I'd like to get back to work.”

Work was all that kept Gordon from despair, in the next days. He plunged into it as one might take a drug or drink. It kept him, for a little of the time, from remembering.

But at night, he remembered. He lay sleepless, looking out his window at the bright stars that to his mind's eyes were always mighty suns. And always, Lianna's face drifted before his eyes.