Hole hunters would depart Pluto and accelerate to the limits of engine power, then coast for ten to fifteen years, keeping an eye on the mass detector. Sometimes they would be half a light-year from Sol before they had to decelerate and turn around. Less mass equalled more range, so the solitary hunter was the rule.

Teaming of ships had been tried, but teams that discovered a hole seldom came back together. One of them tended to have an accident. Hole hunters were a greedy lot, self-centered and self-sufficient.

Equipment had to be reliable. Replacement parts were costly in terms of mass, so the hole hunter had to make an agonizing choice with each item. Would it be better to leave it behind and chance a possibly fatal failure, or take it along, decreasing the range, and maybe miss the glory hole that is sure to be lurking just one more AU away? Hole hunters learned to be handy at repairing, juryrigging, and bashing, because in twenty years even fail-safe triplicates can be on their last legs.

Zoe had sweated over her faulty mass detector before she admitted it was beyond her skills. Her primary detector had failed ten years into the voyage, and the second one had begun to act up six years later. She tried to put together one functioning detector with parts cannibalized from both. She nursed it along for a year with the equivalents of bobby pins and bubblegum. It was hopeless.

But Shirley Temple was a palace among prospecting ships. Having found two holes in her career, Zoe had her own money. She had stocked spare parts, beefed up the drive, even included that incredible luxury, a lifeboat.

The lifeboat was sheer extravagance, except for one thing. It had a mass detector as part of its astrogational equipment. She had bought it mainly for that reason, since it had only an eighteenmonth range and would be useless except at the beginning and end of the trip, when they were close to Pluto. It made extensive use of plug-in components, sealed in plastic to prevent tampering or accidents caused by inexperienced passengers. The mass detector on board did not have the range or accuracy of the one on Shirley. It could be removed or replaced, but not recalibrated.

They had begun a series of three-month loops out from the mother ship. Xanthia had flown most of them earlier, when Zoe did not trust her to run Shirley. Later they had alternated.

"And that's what I'm doing out here by myself," Xanthia said. "I have to get out beyond ten million kilometers from Shirley so its mass doesn't affect the detector. My instrument is calibrated to ignore only the mass of this ship, not Shirley. I stay out here for three months, which is a reasonably safe time for the life systems on Lollipop, and time to get pretty lonely. Then back for refueling and supplying."

"The Lollipop?"

Xanthia blushed. "Well, I named this lifeboat that, after I started spending so much time on it. We have a tape of Shirley Temple in the library, and she sang this song, see—"

"Yes, I've heard it. I've been listening to radio for a very long time. So you no longer believe this is a trick by your mother?"

"She's not..." Then she realized she had referred to Zoe in the third person again.

"I don't know what to think," she said, miserably. "Why are you doing this?"

"I sense that you are still confused. You'd like some proof that I am what I say I am. Since you'll think of it in a minute, I might as well ask you this question. Why do you suppose I haven't yet registered on your mass detector?"

Xanthia jerked in her seat, then was brought up short by the straps. It was true, there was not the slightest wiggle on the dials of the detector.

"All right, why haven't you?" She felt a sinking sensation. She was sure the punchline came now, after she'd shot off her mouth about Lollipop—her secret from Zoe—and made such a point of the fact that Zoe was not her mother. It was her own private rebellion, one that she had not had the nerve to face Zoe with. Now she's going to reveal herself and tell me how she did it, and I'll feel like a fool, she thought.

"It's simple," the voice said. "You weren't in range of me yet. But now you are. Take a look."

The needles were dancing, giving the reading of a scale-seven hole. A scale seven would mass about a tenth as much as the asteroid Ceres.

"Mommy, what is a black hole?"

The little girl was seven years old. One day she would call herself Xanthia, but she had not yet felt the need for a name and her mother had not seen fit to give her one. Zoe reasoned that you needed two of something before you needed names. There was only one other person on Shirley. There was no possible confusion. When the girl thought about it at all, she assumed her name must be Hey, or Darling.

She was a small child, as Zoe had been. She was recapitulating the growth Zoe had already been through a hundred years ago. Though she didn't know it, she was pretty: dark eyes with an oriental fold, dark skin, and kinky blonde hair. She was a genetic mix of Chinese and Negro, with dabs of other races thrown in for seasoning.

"I've tried to explain that before," Zoe said. "You don't have the math for it yet. I'll get you started on spacetime equations, then in about a year you'll be able to understand."

"But I want to know now." Black holes were a problem for the child. From her earliest memories the two of them had done nothing but hunt them, yet they never found one. She'd been doing a lot of reading—there was little else to do—and was wondering if they might inhabit the same category where she had tentatively placed Santa Claus and leprechauns.

"If I try again, will you go to sleep?"

"I promise."

So Zoe launched into her story about the Big Bang, the time in the long-ago when little black holes could be formed.

"As far as we can tell, all the little black holes like the ones we hunt were made in that time.

Nowadays other holes can be formed by the collapse of very large stars. When the fires burn low and the pressures that are trying to blow the star apart begin to fade, gravity takes over and starts to pull the star in on itself." Zoe waved her hands in the air, forming cups to show bending space, flailing out to indicate pressures of fusion. These explanations were almost as difficult for her as stories of sex had been for earlier generations. The truth was that she was no relativist and didn't really grasp the slightly incredible premises behind black-hole theory. She suspected that no one could really visualize one, and if you can't do that, where are you? But she was practical enough not to worry about it.

"And what's gravity? I forgot." The child was rubbing her eyes to stay awake. She struggled to understand but already knew she would miss the point yet another time.

"Gravity is the thing that holds the universe together. The glue, or the rivets. It pulls everything toward everything else, and it takes energy to fight it and overcome it. It feels like when we boost the ship, remember I pointed that out to you?"

"Like when everything wants to move in the same direction?"

"That's right. So we have to be careful, because we don't think about it much. We have to worry about where things are because when we boost, everything will head for the stern. People on planets have to worry about that all the time. They have to put something strong between themselves and the center of the planet, or they'll go down."

"Down." The girl mused over that word, one that had been giving her trouble as long as she could remember, and thought she might finally have understood it. She had seen pictures of places where down was always the same direction, and they were strange to the eye. They were full of tables to put things on, chairs to sit in, and funny containers with no tops. Five of the six walls of rooms on planets could hardly be used at all. One, the "floor," was called on to take all the use.