A/N: An estrus cycle is what many mammals have rather than menstruation. Uterine lining builds up and is reabsorbed without being externally shed. I personally think it makes a lot more sense as compared to our own deeply inconvenient system.

7

From that day on, Xen began to plan for her visit to Underworld. She made lists of the things she would need: a map, good shoes, money, a hat to keep the sun off her head, some way to protect herself without the two bots. She kept poring over Dr. Montalban's notes, trying to find some clue.

By the time she was eleven, by which time she had seen Bob Masterson dozens of times but no one else even once, she had found a secondary override. She didn't use it right away. She was impatient, but not so much that she would risk hurting the two most important people in her world. Editing the bots' primary directive would be dangerous if she did it incorrectly, and she would have to add a lot of qualifiers for it to really work. For instance, her first idea was to order them not to leave the Lab except under her instructions or in case of immediate threat to the Lab or themselves. Then she thought about Tori's typical reasoning plus her current set of priorities and added a prohibition against causing an immediate threat to the Lab. It took her years to get through this process.

In the meantime, she finished her first robot, a thing about the size of a radroach and the same general shape. It couldn't fly. She hadn't been able to put together a propulsion system sophisticated enough yet. She named it Roach 1 and, once the novelty of having it scuttle around the lab wore off, sent it out into the tunnels with a forward camera sensor to map the Metro in a widening circle around the Lab. It got quite a few miles out before it was destroyed by a roving pack of Ghouls. Xen found the footage very interesting.

Tori helped her tan a mole rat hide to make her first pair of simple moccasins. "It'll be easier for you to walk softer in these," she said. "It's about time we started doing some stealth lessons with you. If you're going to keep going outside, you'll have to be able to hide."

When she was twelve she asked Bunni about sex. She had read all the material in her encyclopedia on the subject, including detailed specifications regarding human biology and physiology, but it seemed to leave some things out. Bunni was not very helpful, since the things Xen wanted to know mostly weren't things a robot would know. Tori didn't know much more, and she promptly deleted a large section of Dr. Montalban's personal archive shortly after that. Xen managed to rescue a couple of videos and several pictures. She examined them closely, but was unable to determine their use or significance until she was thirteen and a half (around the time Roach 2 was destroyed under similar circumstances to those that had "killed" Roach 1).

The robots were surprisingly sensitive to her need for more physical privacy. This also made it easier to proceed with her programming research. Roach 3 had a small offensive laser and a much better defensive avoidance routine than Roach 2. It killed one feral Ghoul and scared off the other one before proceeding on its outward-bound journey. By that time, she was in good enough shape to walk ten miles in a day, though it wasn't easy or fun. She was never able to run very far or fast. It hurt her feet and knees.

"Concrete's not too easy on human locomotive systems," said Tori. "Beats me why they built so much of it. Anyway, there's not much you'd actually be able to run away from. The only way to win that game against a yao guai or a deathclaw is not to play."

"I can sneak past the sentry bots now," Xen pointed out.

"Sentry bots can't smell worth a damn," said Tori. "When you can sneak past Bunni, then I'll be impressed."

When she was fourteen she had her first and last growth spurt, which shot her from four and a half to five feet one inch tall in just a few months. She was constantly hungry and tired. Bunni and Tori did a few blood tests to check her hormone levels, since she hadn't shown any signs of developing a menstrual cycle.

"I'm afraid we have bad news, Xen," said Bunni.

"What?" Xen asked, scooting to the edge of the chair. "Am I sick?"

"No, Dear," said Bunni. "You're very healthy. The fatigue will go away now that you've stopped growing. It's just that your individual biology is too unusual for you to experience a human reproductive cycle. Your estrogen levels are somewhat low and the xenoorganic analogue, while present, appears to be trying to orient you toward an estrus rather than a menstrual cycle. As a result you seem to have developed some androgen insensitivity."

"So what does that mean?" asked Xen.

"It means you'll still like boys, but you're sterile," said Tori.

"Insufficient data error," said Xen, repeating something she had often heard the others say. "You mean my eggs are bad?"

"I mean you have no eggs," said Tori. "Your ovaries are just barely up to cranking out the amount of hormones you need to stay healthy and look female. Sort of. You're probably going to stay thin and kind of flat."

"That could just be Doctor Graber's genetic contribution," said Bunni. "She was a slender person."

"What about the artificial womb?" Xen asked. "I could make a baby with the frozen stuff we've still got plus a somatic cell from me, couldn't I?"

"It's possible, Dear," said Bunni. "But it would take a long time. Remember, it took nineteen tries and years of work before you were born."

"More babies in jars," said Xen. "Ew." She thought about it for a minute. "Well, I don't think I really want to have a baby. I wouldn't know how to take care of it."

"I do," said Bunni. "But I agree that now is not the time."

"Your chromosome length says you're going to have a good long life, if you manage to outlast the allergies," said Tori. "Plenty of time to worry about that later."

Xen abandoned the subject with some relief and went to work on another type of robot. The third bot in the Roach series was still viable, as far as she knew, but was rapidly approaching the outer limit of its signal strength. She had instructed it to return by the shortest possible route. Her current project had more to do with her long-term plans.

"It's gonna be a bitch to write a nav program for three legs," said Tori, handing her a very small soldering iron.

"They're just for holding," said Xen, applying the blue flame carefully. "I'm hoping to cannibalize the hover unit from one of the old cars next time we go out."

"Won't that be a little overpowered for something this size?" asked Tori. The cylindrical chassis Xen had built was a little smaller than Tori's central "head." The main sensor and laser unit were in a rough dome on top, and the three legs stuck out around the bottom of the main cylinder. Each one had a simple grasping manipulator and two joints, one at the body and one in the middle of the limb.

"It needs to be able to carry things for me," said Xen. "I want to do some walking out in the tunnels."

"Don't go all wetware logic malfunction on me just 'cause you're a teenager now," said Tori. "It's not like I'd let you out there without one of the sentries."

"I know," said Xen. "But they're not built for added weight and I don't want to impair their mobility. This will have a small laser and a big propulsion unit. If I mount a sling under it, it can even carry me."

"Except for the small problem of the exhaust," said Tori.

"Oh," said Xen. "Yeah." She looked at the chassis thoughtfully. "I could aim it out to the sides. Three exhaust pipes. Then it'll have better attitude control, too."

"Whatever works," said Tori. "I'd put a dish under it, too, though. Reflect the heat away from the payload."

"I like that idea," said Xen. "Maybe we can bend a wheel well into the right shape."

"Can't hurt to try," said Tori. "You write the main drivers yet?"

"No," said Xen. "I think I've got a good enough handle on Dr. Montalban's work to use one of his simpler AIs for it. It's the first one he made for Tawnee. That way it can process multidirectional sensor inputs. Not as well as you do, but well enough not to run into things."

"Oh, I'm not worried about being replaced," said Tori. "I'm not equipped to be as emotional as Bunni is."

"I noticed," said Xen dryly.

"Hey, you should consider yourself lucky my AI doesn't go all suboptimal when you're not happy. You'd have grown up a total brat if I was as soft as the Robobrain."

"Which is why they gave her to me to care for, not you," observed Bunni from the doorway. "You would be a totally inadequate parent if I weren't here."

"Course I would," said Tori. "I'm a lab assistant. That's why I exist."

"I like you both," said Xen.

"Of course, Dear," said Bunni, and opened her tentacular arms. Xen gave her a hug, and felt so guilty that she did no more work on her reprogramming research for almost a week.

Then came the day when she found out about Recon Craft Theta.

She hadn't actually looked at much of the Doctors' biology research. Most of her knowledge in that subject was from materials they'd brought to the Lab for their own reference. There were several reasons. Most of the notes were about Xen, which bothered her. She'd always left concern over her medical welfare to Bunni and Tori. Sometimes she didn't really like the reminder that she was what Tori called wetware. And, except for some information on the maintenance and functioning of the artificial womb, all of the research notes were by Doctor Graber. She felt a peculiar distaste for anything set down by the person who had tried to kill her and who had killed her other genetic contributor. She couldn't see the monster of her earliest nightmares as the sole producer of anything good.

It was actually from Dr. Montalban's maintenance logs that she first found a reference. He'd recorded a series of pH readings from the first few unsuccessfully implanted embryos. There was nothing special about this, up until the portion that said:

It is unfortunate that the containment suit the xenoorganism originally was found wearing at the crash site was not retained. At the time, it was deemed too bulky and heavy for the available space, and the body wouldn't fit into the field station with it on. Useful pH readings from some of its systems might have been...

But Xen had stopped reading. "Crash site?" she said. She'd never really thought about where her third genetic contributor had come from. All her life he'd been inside the field station, unliving and unchanging with his permanently swollen right eye.

She ordered the computer to search Dr. Graber's notes for the relevant phrase. That got her a location, a mention of the radio signal they had tracked, and a note of the xenoorganism's condition upon recovery, something to the effect that "decay apparently was completely retarded by the containment mechanisms of the garment."

Try as she might, she could find nothing else about what had crashed or what the suit was made of, or any other clue to where the xenoorganism had come from before Recon Craft Theta found its final resting place well to the north of Washington, D.C.

"Bunni," she said. The robot entered on soft treads.

"Yes, Xen?"

"Where did my third genetic contributor come from?"

"Unable to process request," said Bunni. "I'm afraid I don't know, Dear. The Doctors were hoping their experiment would teach them about his planet by teaching them about his physiology."

"But it didn't work," said Xen.

"Not really, Xen. They couldn't clone him without the clone dying from Earth's pathogens before it even had very many cells, and there was only so much they could learn from a dead body. He breathed oxygen, had iron-based blood cells, and had most of the same organs as a human person. The rest of the experimental results they recorded before their deaths are biochemical. But I see you've found those."

"Yes," said Xen. "But I want to know where he came from."

"No one can tell you that, I'm afraid," said Bunni. "His species have not visited here frequently. And if they did, I'm afraid they might have the same attitude toward your genetic composition that Dr. Graber did. If they are genetically close enough to produce a viable hybrid, their psychology is probably close enough for them to be xenophobic as well."

"But you don't know that," said Xen.

"No," said Bunni. "The data is insufficient. But I would hate for you to be hurt or disappointed, Xen."

"I know," said Xen, and hugged her again.

But guilt had lost out to something more compelling. She resumed her AI research and added a considerably longer trip to her future itinerary. After two decades, the craft might or might not still be there. It had been far out in the woods, away from human settlements, and it wouldn't have been easy for anyone to move something so big. Either way, she had to know. Maybe in Underworld I can find someone who knows more about the route from here to there. Pay them for the information.

At that point, she had no plans to take anyone with her. Bob Masterson was nice enough, but he was nothing at all like Xen or either of the Doctors. She knew Tori didn't think he was trustworthy, and if he wasn't, who would be? She didn't want to be alone with a stranger out in the wilderness under that huge and frightening sky. It was bad enough in the City, where she could pretend the buildings were walls and the sidewalks were floors. Even with her unsleeping packbot and its laser, it wouldn't be hard for an armed and combat-experienced human to do basically as he wished with them.

I'll have to find a way to stealth the packbot.

But first she mounted a more powerful transmitter on Roach 3, recharged its laser, and sent it to map the way to Underworld.