Zi said with clear embarrassment, "Of course, there's nothing to be afraid of, but I never saw a Mentor before. We only receive verbal messages and there are no pictures of them in our books. This is most unusual…and a gr-reat honor, I think."

"But Zi," said Jeff, "how can you be afraid? We humans have always imagined dragons to be completely brave. It was dragons who terrified others. Dragons could even breathe fire."

"Oh, we can do that." said Zi, not taking her eyes off the apparition on the screen. She breathed out a small blue flame. "That's one of our old, primitive defenses, but it takes a lot of energy to separate the hydrogen from the…"

Jeff had backed away from her. "There! You see! Even though you're small, you shouldn't be afraid."

Zi said, indignantly, "I am not small! Only the Grand Dragonship is larger than I am, and she's my aunt. And I'm not afraid of the Mentor-if that's a Mentor. I'm just overcome by respect and awe."

But she acted afraid.

Jeff shrugged and turned back to the screen. The strange figure was staring at them, if those patches of shimmering color were indeed eyes.

"What do you want?" Jeff demanded, determined that he wasn't going to show fear, whatever the others did.

"Courtesy and respect," said the figure in a kind of creaky voice, as though it were something that was not often used. "I've summoned you to the presence, and you have not hurried. See to it that you come immediately to the Mentor castle on the hill. Alone!" The screen went blank.

Norby's head popped up. "Not without me."

"I thought you were too scared," Jeff said.

"I am, but I'm less scared when I'm with you. Besides, if we're together we can both escape through hyperspace. If we were separated," he added virtuously, "I wouldn't dream of escaping on my own and leaving you in danger here."

"We'll think about escape later," Jeff said, "after we find out what the Mentors want. Come on, partner!"

Jeff wanted to pretend that Norby didn't have antigrav but this had disadvantages. The path up the hill to the large castle was steep, and the paving was ravaged by age. It was rough and uneven, and rank weeds grew in the cracks.

Jeff sighed inwardly at the discomforts of their progress, while Norby, walking on his two-way feet, complained loudly and repetitiously until Jeff finally decided that carrying him was easier than listening to his grumbling.

Halfway up, Jeff was forced to say, "You're no pleasure to carry uphill full weight, Norby, so could I persuade you to turn on your antigrav a little?"

Norby complied with his usual mixed-up judgment of intensity, so that Jeff had to shout, "Not that much," as his feet began to leave the ground. "You'll reveal the ability."

Norby added a bit of weight and they continued to climb.

It soon became quite apparent that the paving was not the only imperfection. What had appeared to be lovely landscaping turned out to be full of flaws, although here and there it seemed as if someone had tried, halfheartedly, to prune trees and weed flower beds.

"The Mentors don't seem to care how things look," said Jeff.

"What's that?" Norby asked, jiggling so much that Jeff lost his balance and let go of him. Whit his own full weight suddenly restored, Jeff sat down hard. Fortunately, he sat on a patch of weeds growing where a paving stone should have been.

Norby came down much more gently. "You keep letting go of me. What's the matter with you?"

"Why were you jiggling? What 's the matter with you?" Jeff got up and rubbed himself where he had made contact with the ground.

"I was looking at that. It startled me. "

Among the flowers off to the side was an odd little metal creature, much smaller than Norby. It had a long arm with pincers at one end, another arm ending in a scoop, and yet another that looked like coiled wire. Underneath were lots of little legs, and the whole thing slightly resembled a Terran crab.

The creature uncoiled its wire, touched Jeff with it, and immediately backed off, waving its other arms furiously.

"We aren't going to hurt anything," said Jeff.

The creature made no sound but turned away and began to weed the garden.

"I think it's just a gardening robot," Jeff said. "It looks very old-all dented and discolored. No wonder the castle grounds aren't in good shape."

"It's not intelligent," Norby said and sailed into Jeff's arms again. "It was nothing for you to be afraid of."

"I'm not the one who…" began Jeff, and then gave it up as a bad job.

They climbed on to the castle until its gigantic metallic door loomed ahead of them. It had hinges, but no doorknob.

"Do we knock?" asked Jeff, "I don't see signs of a computer scan."

"You might not recognize one on this planet," Norby said.

"Well, do you?"

"No," said Norby. "I keep feeling I know this place, but the memory is so faint, it doesn't seem to help me. The diamond design on the door seems familiar."

"That's because it's also on the dragons' collars and on the top of their hassock. Didn't you notice?"

"Come to think of it, I did."

"I'll bet. But now that you do, what does it mean?"

Norby paused. Then he said in a hurt tone, "I wish I weren't so mixed up with Terran parts. If all of me were alien, or Jamyn, I'd probably understand everything."

"I doubt that, somehow, but try to think. Does the design tell us what to do, or is it just the mark of the Others?"

"That's it," Norby cried out triumphantly. "It just came to me like a flash. It's the mark of the Others. Now why didn't you think of that? That's how the Others marked their special property. And if you use the right computer technique, the diamond plus that squiggly border design around the door…"

"It was around the hassock, too," said Jeff.

"I'm glad you noticed," said Norby. "Well, the diamond plus the squiggly border design tells you how…"

"Tells us how to what?"

"I'm sorry, Jeff, but that's the part I can't remember."

And just as Jeff was going to express his opinion of that, the massive door began to creak slowly open. Jeff could see nothing inside but a long, dark hallway.

"Well, let's go in, Norby."

Norby took a step backward. "Do we have to?"

"Certainly. That's what we came for." Jeff strode boldly through the door and down the hall, looking for an opening into a room. Norby ran behind him, mumbling.

"What are you talking about?" asked Jeff.

"I'm not talking. At least, not words. I'm going over equations that keep popping into my head. I think the squiggly design is a set of mathematical relationships. I've got to figure it out. I want to understand myself so I don't keep getting into trouble, like landing in the Coliseum by mistake."

"The old building on Columbus Circle in Manhattan? Why " did you land there?"

"No! The one in Rome," said Norby impatiently. I told you all about it in hyperspace. "

There didn't seem to be any doors, and the corridor began to wind.

"I couldn't understand you in hyperspace. When were you in Rome?"

"When I got the lion. Don't you remember the lion? It was all very unpleasant in the Coliseum. People were fighting in armor and other people were being eaten by lions. Then guards picked me up because I was in the way and threw me into the lion's cage…"

"Norby! Was the Coliseum-intact?"

"Sure. Not at all like the ruin in the pictures of Rome."

Jeff stopped short before another sharp curve in the corridor. "Are you telling me the truth, Norby? We were studying Roman history and you were working with Shakespeare's Julius Caesar. So when you left…Norby! You couldn't have."

Norby said, "Well, where did the lion come from? I was thinking how nice it would be to see old Julius himself, and maybe I didn't quite make it and was a century short-a century later in time than Julius-with Christians being thrown to the lions, and one of the lions came with me."