“But, Dad—”

  “Jackson,” Dad said, and now his voice was tender and loving. This was how Dad had sounded to Jackson when he was a little boy. “I’m trying to keep you alive.”

  How could Jackson argue with that?

  I’m sure Dad was telling the truth about not learning anything about Mammoth Cave or people living nearby, Jackson thought as he opened the door again and started struggling around to the back of the van. But . . . is there something else that he did find out? Something that’s too horrible for him to tell me?

  NINE

  Eryn

  “If you’re still here next fall, you are going to want to remember this spot,” Lida Mae said, planting her feet in the exact middle of the trail. “There are pawpaw trees there, there, and there.” She pointed at three leafless trees, though Eryn couldn’t tell any difference between their bare branches and any others. “And eating pawpaws is like dying and going to heaven. Without the dying part, of course. Best fruit ever.”

  Next fall? Eryn thought.

  “I’m sure—” she began.

  “I’m sure these woods are beautiful in the fall,” Ava interrupted.

  Eryn had intended to say, I’m sure we aren’t still going to be here next fall. Because it wasn’t possible. Was it? Surely the grown-ups had planned to stay in the woods for only a week or so, until all the attention Nick and Eryn had gotten back home had blown over and everyone could go back to living normally, just keeping certain facts about Ava and Jackson secret, like always. The papers Nick and Eryn had found in the secret room complicated things, but once the kids were home again, maybe they could do some secret computer searches and solve the dilemma of the papers that way.

  It was funny how, now that it was daylight, now that she’d walked a little, and now that she’d had breakfast (however pitiful), Eryn could see some fairly simple solutions to her problems.

  She longed to be able to deal with the papers just by doing a few computer searches. Preferably while sitting in her own warm room at home (at either Dad’s or Mom’s house—it didn’t matter which) with all the knowledge of civilization at her fingertips. From the first moment she’d laid eyes on the secret papers from the secret room, she’d been certain that there had to be some way out of the dilemma other than actually destroying all the robots in the world. A computer search could help her and Nick find that way, right?

  If there’s any way to keep that search secret, she thought.

  And if they could figure out the mystery of Lida Mae, whose very existence seemed to defy everything Eryn had come to understand either from the robot adults she knew or from the messages left behind by the humans of the past.

  Eryn grudgingly decided that she should be glad Ava had interrupted before Eryn could say something snobby or bitter about Lida Mae’s woods. She didn’t want Lida Mae running off again.

  But having Ava along meant that Eryn and Nick couldn’t just come out and say, Lida Mae, have you seen the secret room in the cave with its secret papers talking about robots?

  Eryn wasn’t sure she had the nerve for that anyhow.

  What if she or Nick or Ava said something that scared Lida Mae away again, and they were left lost and far from the campsite? Something like Are you descended from the people who wrote the papers we took from the secret room? Does that mean humanity didn’t die out after all, so robots weren’t as dangerous as everyone thought? So there’s no need for Nick and me to destroy all the robots now?

  Those were the kinds of questions Eryn really wanted answered.

  “How do you pick the . . . what are they called?” Nick asked. “Pawpaws? Is there some kind of machine you use?”

  Oh, good try, Nick, Eryn thought. Way to find out what kind of technology her family has! Way to inch toward the information we really want to know . . .

  It would only take about a million years to get there.

  Lida Mae giggled.

  “A pawpaw-picking machine? What a thought,” she said. “Nah, you do it by hand. They fall to the ground when they’re ripe—any machine would crush them. Though if you’ve got little brothers or sisters or cousins, they’re good for picking up pawpaws. Being so low to the ground and all. That’s kind of like having a picking machine.”

  “Do you have lots of little kids in your family?” Eryn jumped in.

  “Oh, you know how it is with little kids,” Lida Mae said with a vague wave of her hand. “One or two of them can seem like a dozen, the way they run around. Makes it hard to count.”

  Did Lida Mae even know how to count?

  Eryn couldn’t think of a way to ask that without sounding insulting.

  They tramped on down the trail. As far as Eryn could tell, it looked no different from the trails they’d hiked the day before, coming from the road to their campsite: dead leaves underfoot, dead-looking leafless trees on either side.

  “What are we close to right now?” Eryn asked, trying to sound casual. “The cave? The cave entrance?”

  Lida Mae snorted, sounding just as amused by Eryn’s question as she’d been by Nick’s.

  “Mammoth Cave goes on for more than four hundred miles,” she said. “And there are something like thirty entrances. It’s right below us. You’re on top of some part of the cave anywhere around here.”

  “Is it safe to walk on top of the cave?” Ava asked. “Is it safe to live here? Is anyone’s house nearby?”

  Is that too dangerous a question? Eryn wondered. Too close to Nick’s question that made Lida Mae run away last night?

  Lida Mae just shrugged.

  “Cave’s a long way down,” she said. She grinned mischievously. “Don’t worry—no one’s going to fall through. Not even if you jump up and down and try. And we’re not disturbing anyone, walking here.”

  That’s not what Ava asked! Eryn wanted to scream. This is impossible!

  She put her hand on Nick’s arm and held him back as Ava and Lida Mae walked on. Once they were a few paces behind, she whispered, “She’s got to start giving us better answers! So we have to start asking better questions! Harder questions that might make her run away again . . . Would you be able to find a way back to the campsite if she did that?”

  “Um . . . maybe?” Nick said, looking back down the trail. “Didn’t we turn right and then left and then . . .”

  Eryn was pretty sure it had been a left turn first.

  “GPS would really help right now!” she fumed.

  “But couldn’t someone track us if we used GPS?” Nick asked.

  By someone, Eryn knew he meant the robots outside the park. Every robot in the world, actually, since they were all linked.

  “Wasn’t that why Mom destroyed everyone’s cell phones yesterday when we got to the nature preserve?” Nick went on. “Isn’t that why the adults are avoiding the robot network, out here in the nature preserve, so we’re all off the grid?”

  “Yes,” Eryn muttered.

  “Do you think the adults are . . . okay . . . away from the network?” Nick asked. “Mom and Dad and Brenda all looked kind of sick when we left.”

  Eryn didn’t like how that sounded: as if she and Nick and Ava had just abandoned their parents when they needed help. What if the adults needed someone to take their temperature or bring them warm soup? Or . . .

  Eryn realized she’d started thinking of her parents as human beings once again. Whatever need they had for soup—or any food—was just a pretense. Just a way they’d been designed to fool their children into thinking they were human. And Nick and Eryn had been completely fooled until the day they met Ava and Jackson, not even a week ago.

  As far as Eryn knew, all the other humans in the world were still fooled. That would be all the other kids in the world who were twelve and under, except for Ava and Jackson.

  And does that include Lida Mae and all her brothers and sisters and cousins? Eryn wondered. Do they know about robots or not?

  Eryn just didn’t know how to think about Lida Mae and her family. It always
made her irritable not to know things. And the more she found and saw and experienced here in the nature preserve, the more clueless she felt.

  “I’m sure the adults will be fine,” she huffed to Nick.

  Several paces ahead, Ava turned and peered back at Nick and Eryn.

  “Are you two getting tired?” she asked. “Do we need to stop and take a break?”

  “Sorry,” Eryn said. “We’re not tired. We were just being slow because . . .”

  “Because we were looking at all the different kinds of leaves on the ground,” Nick finished for her.

  Eryn flashed her brother an I owe you one look. She just hoped Ava and Lida Mae didn’t notice.

  “Lida Mae’s been telling me how some of the vegetation around here can be used for medicine. And some can be food that tastes a lot better than you’d think,” Ava said, making it sound like she’d actually been interested in hearing about trees.

  Eryn didn’t have the patience for this.

  “You know what I was thinking?” she said, picking up her pace to catch up with Ava and Lida Mae. Nick trailed just a step or two behind her. “We’re having this nice hike with you today, Lida Mae, but what if we want to hang out with you tomorrow or the next day or the day after that, and we haven’t made plans ahead of time? Or what if we make plans, and then someone gets sick and needs to cancel?”

  “How would we get in touch with you?” Nick finished for her, and she shot him another grateful look.

  “Oh, goodness, we can make plans for all sorts of hikes and outings, any day you like,” Lida Mae said. “We can plan all that ahead of time. I don’t have to ask permission. Mammy and Pap let me roam anywhere I want, as long as I get my chores and lessons done each day. And don’t worry—I almost never get sick.”

  That wasn’t the point! Eryn wanted to shout.

  “Back home we can communicate between, say, our house and the houses our friends live in, even if they’re a long way away,” Nick said, taking up the cause.

  Oh, good grief, Eryn thought. Is he going to suggest smoke signals between our campsite and wherever Lida Mae lives? Does he think it’s worth it to work so hard to get one little scrap of information, like what direction Lida Mae lives in, starting from the campsite?

  That would be more useful information than they’d gotten out of Lida Mae so far. Maybe they could work up from there to talking about text messages and e-mail and computers . . . and robots.

  “Oh, you mean, you use a telephone?” Lida Mae asked.

  “You know what a telephone is?” Eryn asked, gaping at the other girl. “Do you have one?”

  Lida Mae rolled her eyes and smirked.

  “Now, what need would my family have for a telephone, when they don’t have any desire to go contacting the outside world?” she asked.

  “To talk to, uh, your aunts and uncles and cousins in their houses?” Eryn asked.

  “Now, that’s just silly,” Lida Mae scoffed. “Why would we need a phone when my whole family all lives so close to each other we can just drop by anytime we want?”

  “That’s the kind of thing we mean,” Ava said, smiling sweetly. “We can’t do that. Because we don’t want to be rude, of course, but also . . .”

  Don’t say it! Eryn thought at Ava. Don’t say, “Because we don’t know where you live,” because that’s going to scare her away again!

  “Well, actually, we could use these,” Lida Mae said, reaching into a pocket of her skirt and pulling out a palm-size object. “I was going to offer this later, but now’s as good a time as any. Have you ever seen a walkie-talkie before?”

  TEN

  Nick

  Ms. Girl Who Dresses Like It’s the 1800s is asking us if we’ve ever seen a walkie-talkie? Nick thought.

  Then he got a good look at the object in Lida Mae’s hand. It wasn’t like any electronic gear he’d ever seen. Rather than rubber or plastic, the outer covering of the walkie-talkie looked like walnut shells pieced together. The antenna looked like an old rusty nail bent into an arc.

  Or maybe it was a miniature horseshoe.

  “You’re just playing with us, right?” Nick asked, before he had time to think. “No way that actually works.”

  Lida Mae’s face flushed.

  “Of course it does,” she said. “Not inside the cave, usually, because you need more of an open range. But out here the signal can go for miles. Here. I’ll prove it.”

  She handed Nick the walkie-talkie and pulled a second one from another pocket.

  “Hold it up to your ear and listen,” she said.

  She ran a ways up the trail, rounding a curve so Nick could no longer see her.

  Nick got a bad feeling in his stomach.

  “Nick! Do what she says!” Eryn hissed at him, lifting his hand toward his ear and pressing her own ear toward the “walkie-talkie” too.

  “See? Do you believe me now?” came rumbling out of the walnut-shell walkie-talkie. Lida Mae’s voice was staticky and hard to understand, but the walkie-talkie definitely worked.

  “Yes!” Nick called out to her, trying to throw his voice hundreds of feet ahead on the path.

  “Press in the nailhead on the side and tell me that way,” Lida Mae whispered back through the walkie-talkie.

  Nick saw the nailhead she meant.

  “You’re right!” he said, in a reasonably normal voice. “You win!”

  Eryn pulled his finger off the nailhead.

  “How do walkie-talkies work?” she asked quietly. “Do their signals travel by satellite? Would anyone . . . outside . . . be able to hear Lida Mae’s family using these? Or us?”

  “Walkie-talkies use radio signals, not satellites,” Ava said, like someone reciting a lesson in school. “Nobody could eavesdrop unless they were in range. Which means they’d have to be in this nature preserve to hear.”

  Eryn and Nick both stared at her.

  “What?” Ava said. “I have a good memory. I know stuff like that.”

  “Never mind,” Eryn said.

  Nick realized it had been a few moments since Lida Mae had said anything over the walkie-talkie. And he couldn’t see where she’d gone. He pressed the nailhead on the side again.

  “Uh, Lida Mae?” he said, trying to keep the nervousness out of his voice. “You’ve proved your point. You can come back now.”

  Silence.

  “Lida Mae?” he called again, shouting this time.

  Birds chirped in the trees. The wind blew, ruffling the dead leaves on the ground. Lida Mae didn’t answer.

  “She wouldn’t have gone off and left us just because Nick didn’t believe her,” Eryn said. “Would she?”

  “Let’s go catch up to her,” Ava said.

  They hustled up the trail, practically running. They rounded the curve that had made the rest of the trail disappear.

  Lida Mae was nowhere in sight.

  ELEVEN

  Ava

  Ava had strange thoughts sometimes.

  Watching Nick talk back and forth with Lida Mae, she hadn’t decided, Oh, right, that means that primitive-looking walkie-talkie really does work. Amazing! She’d thought, How would Jackson and I fake something like that, if we wanted to fool Nick and Eryn, just for fun?

  She was pretty sure her own enhanced hearing would have allowed her to dash a half mile up the trail and hear anything Nick said, even if he spoke in a whisper. She and Jackson had played around with ventriloquism once—being homeschooled and trapped in the house with Mom all day sometimes made them desperate for entertainment. Ava hadn’t had much talent for it, or liked it enough to keep practicing. But for a week or two Jackson constantly played pranks like pretending to yell from upstairs, “Ava! Get up here quick! You’ve got to see this!” when he was really hiding behind the couch. He only stopped when Ava confronted him: “Did you alter your voice box so you’re transmitting by radio waves somehow, to be so good at that? You know, if Mom or Dad figure out what you’ve done, they may start examining all your circuits and find out
what you did to your sight and hearing. And then—back to ordinary for you!”

  But Jackson and I always try as hard as we can to seem like normal human beings anytime we’re around humans, Ava thought. For years our lives have depended on that. What’s Lida Mae trying to prove? Or hide? Why would she want us to think her family has the technology to make walkie-talkies if they really don’t?

  Ava reminded herself that, as far as she could tell, Lida Mae was human. Her eyes looked like human eyes, her movements were completely free of jerkiness—and she raved about pawpaws, of all things.

  What if she and her family are humans who . . . evolved? Ava wondered.

  She wasn’t sure how many generations ago Lida Mae’s family might have been cut off from the rest of humanity.

  It had to have been before the rest of humanity ended, Ava thought grimly.

  That was centuries ago. Was that enough time for Lida Mae’s family to have developed extreme hearing, along with the ability to throw their voices over a distance of a half mile? Ava tried to think scientifically: Would those adaptations be useful in and around Mammoth Cave?

  It really was simpler to believe that Lida Mae and her family could build walkie-talkies out of walnut shells and rusty nails.

  So why was Ava fighting against believing that?

  Eryn tugged on Ava’s arm.

  “Do you think Lida Mae is coming back?” Eryn asked, clearly struggling to keep the panic out of her voice. “If we’re stranded out here on our own, do you think we could find our way back to the campsite?”

  “Probably,” Ava said, answering both questions with one word. She flipped her uneven braids over her shoulders. The truth was, she would be able to make it back to the campsite blindfolded, because she and Jackson had both added some directional assistance to their brains, along with the other changes they’d made. But it was better not to reveal that unless she had to. “I think Lida Mae’s just playing a prank on us. Or starting a game. Hide-and-seek, maybe?”

  “Eryn didn’t like hide-and-seek even when she was a little kid,” Nick muttered.