The first time Jenny met her grandfather, he slammed the door in her face. She had been brainstorming ideas for her school project, a family tree, and decided to go meet him. After all, Jenny's grandfather only lived a few blocks away, and it was silly that they had never met before.
         So when the bus dropped her off after school, rather than going home, Jenny walked to his house, skipping as she went. Grandpa Abe had a very big house, with a garden out front, lots of windows, and a big brown door with a knocker. Jenny was scared as she walked forward, thinking that the house might be haunted, but she didn't turn back.
          The knocker was heavy, but she slammed it three times, and when the door finally opened, an old man with gray hair, a thick beard, and even thicker glasses was glowering down at her.
         "What do you want?" he demanded.
         "Hi," Jenny said. "We never met before, which I thought was silly, but my name's Jenny, and you're my grandpa." She thought it appropriate to shake his hand, so she put out hers, and Grandpa Abe stared at it, looking as if he had seen a ghost.
         "Never come here again," he said, with a haunted look on his face, and then he slammed the door.
         That was how Jenny met her grandfather.

         Jenny's father was angry that she had gone to see Grandpa Abe. He said there were a lot of things she didn't know, and their family doesn't talk to Grandpa Abe anymore. He said Grandpa Abe doesn't like visitors, and Jenny mustn't go back to his house under any circumstances. As Jenny's father said all this, Jenny tugged at the end of her necklace, where there hung a tiny mechanical butterfly. It was made of little silver cogs and gears, and Jenny had worn it ever since she could remember.
         "Do you understand what I'm saying?" her father said when he was done. Jenny nodded. "I'll explain everything when you're older, but for now, please trust me. Your grandfather is old and grumpy, and he just wants to be left alone."

         Jenny wasn't planning on visiting her grandfather again, but when the bus dropped her off the next day, she walked the six blocks to his house. It wasn't fair. Just because he was old and grumpy didn't give Grandpa Abe the right to be so mean. And he was her grandfather, which meant he had known Jenny's mother. Jenny had a lot of questions about that.
         This time Grandpa Abe saw her through the window and met her on the porch.
         "What are you doing here?" he asked. "I told you never to come back."
         "I know," Jenny said, "but I have this project for school, and I thought you could help, and you are my grandpa, aren't you?"
         "Get out of here," he said. "Get out of here now."
         Jenny started to cry. She clutched her necklace, and Grandpa Abe's eyes lit up when he saw the mechanical butterfly.
         Suddenly, he didn't look so grumpy anymore. He came down the steps and put a hand on Jenny's shoulder. "Please stop," he said. "I just don't like visitors. That's all."
         "But you're my grandpa," Jenny said, her hand still on her necklace.
         He nodded. "Makes no difference. I don't like to be bothered." Jenny was still sad, and Grandpa Abe's eyes never left the necklace.
         "If I help you with your project," he said finally, "when we're done, will you promise never to come back here again?"
         Jenny nodded happily, said, "Sure thing, Grandpa Abe," and ran through the open door before he could say another word.
         He grunted, muttering to himself about how this was a mistake, and followed her inside.

         They worked on the family tree all afternoon, and Grandpa Abe told Jenny about all of the relatives she had never met.
         "And that brings us to your mother, Erin Morgan. Put that on the branch right there. She married your father, James Isaacs, and together they had you. There, that's the end. You're done now, right?"
         Jenny was staring at the paper. "But if my mommy's name was Erin Morgan," she said, "why is mine Jennifer Isaacs?"
         "Because when two people marry, the wife usually takes the husband's name," Grandpa Abe said.
         "Why?"
         "That's just the way it is."
         Jenny looked puzzled. "So before she met my daddy, my mommy's last name was Morgan, just like yours?"
         "Right," Grandpa Abe said. "Is that your last question? Because I think it's time for you to leave. Your father must be worried, and-"
         "One more thing," Jenny said. She walked across the room and into the hallway. "I want to see something."
         "Where are you going?" Grandpa Abe asked. He was nervous.
         The door was open just a crack, but that had been more than enough to pique Jenny's curiosity. Earlier, she caught a glimpse of something inside. Something big. Something fascinating.
         Grandpa Abe moved to stop her, but Jenny was too quick, and before he could reach her, she was already inside with her head tilted back, looking up.
         The machine towered over twenty feet high, taking up almost the entirety of the room. She saw now why Grandpa Abe had been so interested in her necklace. Like the pendant, the machine was made of lots and lots of cogs and gears. Only instead of a butterfly, the machine took the shape of a tree. Interconnecting metal plates kept the trunk together, with enormous wheels spinning one on top of the other, going up and up. Jenny had a hard time gazing into the interior of the tree itself, but she spotted a giant pendulum swinging back and forth. Finally, smaller wheels extended out, supporting branches made up of metal rods, giant levers, and rotating chains.
         Jenny approached the machine, while Grandpa Abe stood off to the side, groaning. The tree was making a lot of sounds-ticking, grinding, pounding, and screeching. Lights were going on and off, and as Jenny stared, looking between the moving wheels and the rise and fall of the pulleys, she thought that maybe she could walk inside.
         "That's enough," Grandpa Abe said, standing between her and the machine.
         "What is it?" Jenny asked.
         "Nothing that concerns you."
         "It's the family tree, isn't it?" Jenny said, jumping up and down. "The real family tree."
         "It's only a project I've been working on," Grandpa Abe said. He led her out into the hallway, and as he closed the door, the blinking lights and turning wheels disappeared.
         "It does something, doesn't it?" Jenny said.
         "That's ridiculous. It's a tree. Nothing more."
         But Jenny was not convinced. "What does it do?" she asked. "Oh, please, Grandpa Abe, tell me!"
         "I already told you it doesn't do anything. Now will you please leave my house?"
         "Okay," Jenny answered happily enough, but before she left, she said, "But I'm coming back. I don't think my family tree project's done yet. Not until I know what your machine does." Then she skipped away, and Grandpa Abe closed the door.

         The next day, when Jenny knocked on the door, Grandpa Abe didn't answer. She could see him through the windows. He sat in his armchair, acting like he was waiting for her to leave. He walked upstairs, where maybe he wouldn't have to listen to the knocking anymore. But she saw him upstairs by the window, looking down at her. She had to stand on her tippy toes just to reach the knocker, but Jenny didn't have a problem with this. She kept on knocking, and Grandpa Abe kept on waiting, until finally he gave up.
         Flinging the door open, he cried, "What do you want?"
         "I want to finish my project," Jenny said.
         "We already went through this. I'm not telling you what the machine does."
         "So it does do something!" Jenny said, giggling. As Grandpa Abe realized his mistake, Jenny slipped into the house and was just as soon inside the room with the machine.
         "What does it do?" Jenny asked, watching the cogs lining up, each gear moving into the next, and the entire mechanism rotating in unison.
         He was beside her now. "I can't tell you."
         "Will you at least let me guess?"
         Suddenly, Grandpa Abe seemed to have an idea. "Yes, you can guess," he said, probably thinking she would never discover the answer. "I'll even tell you if you're right or wrong, but only if you follow my rules." Jenny was looking up, listening intently. "First, you only get one guess a day. And if you use it up, you have to go home. Do you understand?" Jenny nodded. "Second, you only get seven guesses. Seven days. Seven guesses. After that, I'm not answering you anymore. Nod if you understand." Jenny nodded again. "And last, after those seven days are up, you have to promise you'll never come back here again."
         "But Grandpa Abe!" Jenny said. "Why can't I-"
         "If you don't promise," Grandpa Abe cut her off, "then I won't answer your questions, and I won't let you back at all. Now, do you promise to follow my rules?"
         Jenny put a hand over her heart and said, "Cross my heart, hope to die, stick a needle in my-"
         "That's good enough," Grandpa Abe said. "Do you want to guess right now?"
         Jenny looked back at the tree. She put her hands on her hips and stared very closely. Then she said, "I got it! It grows money, doesn't it? You know the saying: money doesn't grow on trees. But yours does! Is that it? Am I right?"
         "Nope, that's not it," Grandpa Abe said. "And since you used up your guess, you have to leave now." Jenny looked disappointed. "Those are the rules." And he led her out, sighing in relief. Six more days.

         The next day was a Saturday, which meant Jenny didn't have to go to school. Her father was asking where she had been going every afternoon, and Jenny didn't want to lie, so she told him about Grandpa Abe and the school project, leaving out the part about the machine.
         "And Grandpa Abe is okay with this?" her father asked, puzzled.
         "Yep," Jenny said. "He's super helpful."
         "Are you sure this is Grandpa Abe we're talking about?"
         Jenny nodded. "Is it okay if I go back this afternoon? He's gonna help me some more."
         "Sure . . ." her father said, still confused. "I guess that's okay."
         That afternoon, Grandpa Abe made a pot of tea and offered her a cup. Jenny liked tea parties, but she didn't like tea, so as they sat at the table, she pretended to sip from an empty cup while Grandpa Abe drank from his.
         "Aren't you going to make your guess?" Grandpa Abe asked after a while.
         "I needed to think a while first," Jenny said. "This tea is super good." She took a sip from the empty cup and turned it upside down. "Can I have some more?"
         Grandpa Abe rolled his eyes, and laughed a little. He poured her another invisible cup of tea, and she took another invisible sip.
         "Your mother liked to pretend to drink tea, too," Grandpa Abe said. "When she was a little girl, maybe your age, we'd have tea parties with all her stuffed animals. I was the only one drinking real tea, of course."
         "Do you miss drinking tea with Mommy?" Jenny asked. Grandpa Abe looked the other way, but he nodded, and Jenny thought about this. "I think I want to make my guess now," she said. "The family tree is a time machine. You're making it to go back and see Mommy again. Maybe you'll even change things so she never went away, if you're allowed to do that."
         Grandpa Abe took a long time before answering. "That's a very good guess," he said, "and I wish it were true. But it's not." And Grandpa Abe took Jenny's cup to the sink. She was hoping Grandpa Abe wouldn't make her go, but then he led her to the door, and Jenny followed, knowing the rules and knowing it was time for her to leave.

         "Why did you make me leave?" Jenny asked the next day.
         Grandpa Abe shrugged and said, "Those are the rules."
         "We were having fun, weren't we? You were telling me about Mommy, and we were drinking tea, and I just wanted to make my guess." Grandpa Abe shrugged again. "You're a mean old man!" she said. "I bet your machine is evil. I bet you're going to use it to destroy the world, because you're sad, and you're mean, and you're evil."
         Grandpa Abe shook his head. "Wrong," he said, and Jenny left and went home.

         The next day was a Monday, and Jenny stopped by her grandfather's house right after school.
         "I'm sorry I got so mad," Jenny said at the door. "I'll follow the rules. I promise."
         Grandpa Abe nodded and let her in.
         Jenny asked if she could see pictures of her mother, so Grandpa Abe brought out the photo album. They sat down on the couch, and Jenny turned the pages while Grandpa Abe explained each one.
         "This was the first time she visited New York," he said, pointing at a picture of a little girl with buildings all around her. "She was four."
         "Her hair is brown and curly, just like mine," Jenny said. Grandpa Abe nodded.
         They looked at another picture of her mother on the beach in Hawaii, and another of her smiling on top of the Great Wall of China.
         "You sure liked to go places," Jenny said. Then she noticed something. In every picture, her mother was wearing the same necklace. She looked more closely and saw the mechanical butterfly. "It's my necklace!" she said.
         "I made it for her," Grandpa Abe said. "Just like the one I made for you."
         Jenny hadn't known this. "Is my necklace special?" she asked. "Does it do anything, like the family tree?" He said nothing, so Jenny continued, "Why did you make it for me, Grandpa Abe?"
         "It was a present," he said. "I gave it to you on the day you were born."
         Jenny was silent. She knew that had been the same day her mother died.
         "I wish I could go back," he said, thinking out loud, and Jenny thought she understood.
         She guessed that the machine was a teleporter and Grandpa Abe was going to use it to travel anywhere in the world he liked. That way he could go back and visit Times Square in New York, lie on the beach in Hawaii, and see the Great Wall of China all in the same day. But Grandpa Abe only shook his head and said, "What a wild imagination you have."

         On Tuesday Jenny saved her guess until late in the afternoon. They played a game of Crazy Eights, which Grandpa Abe said he used to play with Jenny's mom. Finally, she asked, "You're old, aren't you?" He gave her a strange look. "I don't wanna be mean, but you are, and I thought that maybe you're scared. I would be, too. So maybe you made your machine so you wouldn't have to be old anymore. Maybe the family tree keeps you young forever. There's a story about that, isn't there?"
         "The Tree of Life," Grandpa Abe said.
         Jenny's eyes lit up. "So am I right? Does the family tree make it so you can live forever?"
         Grandpa Abe looked down. "That's a good guess," he said, "but no, I don't want to live forever."
         "What do you want?" Jenny asked, but Grandpa Abe looked away, and she knew it was time for her to go.

         On Wednesday Jenny asked to look at the machine more closely. She circled the family tree before deciding to go as far inside as she could. It sounded almost alive, with the bells and whistles going off, the ticking of machinery, and the motion of the wheels. There was a chair in the center, surrounded by lots of wires and cables, and behind it the pendulum was swinging back and forth. Everywhere, the tree was moving, parts revolving, chains whirling, and springs winding and compressing. Finally, Grandpa Abe told Jenny she had had enough time to look.
         "It's beautiful," she said as he led her out the door. Grandpa Abe nodded. "How long did it take to build?" He didn't answer. "I bet it was a long time," she continued. "Maybe the family tree doesn't do anything after all. Maybe you made it because you're sad about Mommy and you wanted something beautiful to make, and maybe that's all there is to it."
         "Is that your guess?" Grandpa Abe asked. Jenny nodded. "Sorry," he said. "That isn't it, either."

         On Thursday Jenny claimed to have figured it out. Grandpa Abe told her to be careful, because this was her last guess, and if she was wrong, she wouldn't have any more chances. So Jenny saved her guess until the end of the day, just in case.
         She looked at the machine one more time, thinking she had missed something. But it was the same as before. A big tree made of plates and wheels and rods. A mess of parts and pieces, like the inside of a clock. Like Jenny's necklace.
         "My necklace!" Jenny said, and clutched the mechanical butterfly. They were in the kitchen, playing Crazy Eights and drinking tea. Grandpa Abe looked up, and Jenny realized she was onto something. "Can you tell me now? Can you tell me what the necklace does?"
         "I already told you," he said. "It was a present."
         "But what does it do?"
         Grandpa Abe said nothing, which made Jenny mad. "Why won't you tell me, Grandpa Abe? I know it does something, just like the machine! Why did you give it to me? Why did you give it to me and then go away?"
         Grandpa Abe was silent for a long time, and Jenny didn't think he would ever answer. But just as she was beginning to cry, he said,
         "The doctors said you were sick." Jenny listened closely. "They told me you were dying, and this made me sad because I was looking forward to becoming a grandpa. I visited you in the hospital. I held you in my arms. You felt weak, and I wanted to make you stronger. So I pressed the mechanical butterfly in your hands, and you lived."
         Jenny was silent for a long time. "That's what the necklace did?" she asked. "It made me live?"
         Grandpa Abe said nothing. He stared at her like he did last week, when they had first met. He stared at her as if he had seen a ghost, and Jenny thought that maybe it was time to make her guess.
         "You're going to bring her back," she said. "That's what your machine does. It makes the dead alive again."
         Grandpa Abe looked terrified. He sat back in his chair, not touching his teacup or the cards. He waited a long time, staring forward, staring through her. Maybe Jenny was the thing that was haunting him. Maybe Jenny was the ghost.
         Finally, Grandpa Abe answered, his voice cracking, "You guessed right."
         Jenny couldn't believe it. She had figured it out! Grandpa Abe was going to bring Mommy back. Jenny couldn't believe it, but he had said so, and it was true!
         "When?" Jenny asked, clutching her necklace. "When can we see Mommy?"
         He looked down and said, "I'm sorry, Jenny, but my plans have changed."
         Jenny didn't understand. "But you can do it, can't you? You can make her alive again?" Grandpa Abe nodded. "Then why won't you?" But he only shook his head.
         Jenny started to cry. Grandpa Abe sat there, motionless, and she thought he was going to make her leave again, which only made Jenny cry harder. But he surprised her.
         "If your father gives permission," Grandpa Abe said, "would you like to stay for dinner? I'm not the best cook, but I'll try anything. Your choice."
         Jenny wiped her tears away. Grandpa Abe had never asked her to stay for dinner before. He had always waited until she made her guess, and he had always asked her to leave after that. But this time Jenny had guessed right. Was that why he had allowed her to stay?
         "What about macaroni and cheese?" Jenny said after a moment. "It's my favorite."
         "That I can make," Grandpa Abe said, and he smiled now, which Jenny had never seen him do before. "That was your mother's favorite, too."

         So Grandpa Abe made macaroni and cheese for dinner, and afterwards they sat on the couch and watched cartoons. Jenny was dozing off, and Grandpa Abe was thinking about carrying her home, but just as the show ended, she said,
         "Maybe it's not so bad that you won't bring her back. Maybe she's not supposed to come back."
         "It would have cost me too much," Grandpa Abe said. "It's a trade I'm not willing to make anymore. That's why I can't do it."
         "But you were gonna do it before?"
         "Yes."
         "What's different now?"
         Grandpa Abe said nothing.

         He waited until she fell asleep, and then he carried her home.
         Afterwards, he sat in his armchair for a long time, thinking. He paced around the house, avoiding one room. Then he entered it.
         He watched the wheels spinning round and round, the pendulum swinging back and forth. He looked down to see Jenny's necklace in his hand, and he clasped it in his palm.
         The doctors could never explain it, but in the very moment he placed it in Jenny's hand, Erin died. It was the necklace, Grandpa Abe decided. Something about the clockwork of the design was unique. Something about it was special. Jenny was supposed to die, and Erin was supposed to live, and whatever he had done, Grandpa Abe had switched their fates that day.
         He gazed into the interior of his machine and walked forward. The necklace had been a mistake, but the machine was no accident. If he could just repeat the process, he had told himself, if he could reverse the direction, and if he could wait until the proper moment, Grandpa Abe could take back what was stolen from him.
         He was inside the tree now. The chair was in the center, and he sat down. She was supposed to sit here. In this very spot. He looked from left to right, eyeing the tubes and wires, the straps and needles. Erin's necklace hung on a pipe overhead, the butterfly twirling in the air.
         He had been so close. If Jenny had only stayed out of his life for a few more years, perhaps he could have gone through with it. Perhaps he could have brought Erin back. The time was approaching so fast, he could almost picture himself holding Erin in his arms again. But now every time he tried, he only saw Jenny.
         Grandpa Abe got up and left the room with the machine. He had had such plans. He had had such dreams. Then the girl had come. Too soon. Far too soon. She looked just like her mother, it was almost uncanny.
         He crushed the mechanical butterfly in his hand and went to the garage to retrieve his tools. There was only one thing left to do now, and Grandpa Abe knew that if he didn't do it quickly, he might never do it at all.
         That night, Grandpa Abe dismantled the machine.

         When Jenny awoke the next morning, her necklace was gone. She searched her room all morning, and in the afternoon she walked to her grandfather's house to see if she had left it there. But Grandpa Abe wasn't home, and she didn't feel like waiting, so she slipped through an open window and went inside.
         Jenny gasped when she observed that the family tree was gone. She waited all day for Grandpa Abe to come back and explain, but he never did, and Jenny went home without any answers.
         The next day, her father told her that Grandpa Abe was going away, and they weren't going to see each other for a long time.
         "It isn't fair!" Jenny said. "He never told me about the trade! He never told me what he wouldn't give up."
         All day Jenny tried to guess what the trade was supposed to be, and what had changed, and Jenny came up with a lot of guesses, but no answers. She knew that if Grandpa Abe was really gone, she would miss going to his house every afternoon. She would miss playing Crazy Eights and drinking invisible tea and watching cartoons. And she would miss the family tree.
         "I'm sorry he had to go away," her father said that night as he tucked her in. "Grandpa Abe is a very hard man to understand."
         Jenny nodded, and he kissed her goodnight.
         She never saw Grandpa Abe or the family tree again.