1

Ellie’s legs wobbled and she thought she might puke. The question made her brain hurt: If you traveled into the past for, like, two seconds, how would you know? She closed her eyes and opened them again. She was definitely at home, in the basement, in front of her mother’s lab table. “Mom?” she whimpered. Then she saw the pasta sliding down the wall. This time she bellowed. “Mom!”

Her mother appeared at the top of the stairs, a small woman in baggy corduroy pants and a big sweater, her long, limp brown hair pinned up carelessly. Her face glowed with excitement as she hurried down the stairs. “Ellie, where were you? I have incredible news!” Dazed, Ellie let herself be led to a stool at the table.

Sophia Gray was a brilliant professor of neurophysics at the University of Chicago. But for years, she’d spent all her spare time in her home laboratory secretly tinkering with time travel. Ellie didn’t understand why her mother was obsessed with this line of work. Most people would call it crazy. But Mom seemed mostly normal. If anyone could make time travel possible, it might be her Mom.

A tangle of tiny motors, wires, and plastic bits covered the table. Mom pointed to the small, roundish metal object she called the “gizmo” and gripped Ellie’s hands. “I am so, so close,” she said, her eyes dancing. “In fact, I could travel right now if not for a couple of small details.”

Ellie’s stomach twisted as her mom began to chatter about this and that measurement. “Mom,” she squeaked. “You’re much closer than you think.”

Mom stopped talking and smiled. “Really! It’s nice to hear some support for a change.”

“Listen to me!” Ellie choked out. “I have evidence!” Evidence was everything. Ellie had known this since she was three.

Mom was no longer smiling. “What are you saying?”

Ellie lost it. “I know it works,” she wailed, “because I just did it!”

2

Mom sat, stunned, as Ellie told her exactly what had happened.

“I came home from gymnastics, dropped my bag, and saw this purple envelope on the table by the door.” Good old Dad. Usually his birthday cards were late, mailed from who knows where. “I got some leftover pasta out of the fridge and put it in the microwave. The card’s from Omsk, Mom. Wherever that is. Anyway, I read the card and came downstairs to find you.”

The note said her dad and sister would be visiting soon. Last year’s visit hadn’t been that great. In fact, their visits were hardly ever great. Every time Ellie saw her, Kat was a year older and a year stranger. They talked a little by phone and whatever, but usually they were too many time zones apart to get over the awkwardness. That was because ever since the divorce when they were five, their dad Michael had traveled the world as a cabaret actor and singer, and Ellie’s identical twin sister Kat traveled with him. Yes, that was weird. Sometimes people were shocked when they heard about it.

In fact, the whole divorce thing worked out pretty well. Dad hated Mom’s research, and Mom wasn’t thrilled with Dad’s constant travel, and now things were just easier. If Mom and Dad were happy, Ellie was happy. Kat could order fries in a bunch of languages, but Ellie wasn’t jealous. She would rather be in Chicago with her friends. After a few years, Dad seemed more like a nice uncle she saw now and then, and Kat was more like a cousin. Their visits to Chicago were random fly-bys, usually on the way to somewhere glamorous like Las Vegas or Acapulco

Ellie went on with her story. “Anyway, you weren’t in the lab, so I headed back up. And that’s when it happened. I slipped on the stairs. And I mean, really slipped! Not a big deal. I mean, all those years of gymnastics really paid off. I actually landed on my feet! I didn’t even come close to bumping your table.” She frowned. “The thing is, the linguini kind of did its own thing. The plate flew out of my hands, and a clam—one little clam!—sort of bailed out over the gizmo.” The next part was hard to confess. “I know I shouldn’t have, Mom, but—I tried to wipe off the goo.”

Mom gasped.

“Yeah.” Ellie gulped. “Contact.”

3

Mom put her head in her hands, and Ellie finished her tale. “I was standing there looking at the mess, and then for a second I was like . . . nowhere. Then I was on the stairs with the pasta still in my hands! Then the nowhere feeling started again, and a second later I was back at the table. I saw the mess on the wall and yelled, and—well, that’s pretty much it.”

When Ellie finished explaining, Mom put her arms around her and rocked her back and forth. “I’m so sorry,” she kept saying until Ellie wriggled free. Ellie had always thought when the big moment came, her mom would scream and jump for joy. But there was no jumping for joy.

Instead, Mom sat with her hands over her face. “I could have lost you!” she whispered. She picked up a needle-thin instrument and inserted it into the machine. Something clicked, and they both sighed in relief. “There’s no way you’re flying off again,” said Mom. She turned to face Ellie. “I could wait until you’re older to finish this.”

Ellie noticed that Mom hadn’t offered to quit. She had only offered to wait. She always said her girls were the most important thing in the world to her. Ellie also knew that without that machine and all the possibilities it contained, her mom would be sad the rest of her life. But why? Why time travel? What did she think was waiting for her out there in some other place and time? Ellie couldn’t understand why she couldn’t just be happy with the here and now.

Ellie wished she were brave enough to support her mom’s dream. Didn’t she trust her to make sure the machine worked perfectly? As a gymnast Ellie had the courage to toss herself in the air and fly upside down. It boiled down to trusting her coach, her spotters, the equipment . . . and physics. And while she didn’t know squat about physics, her mom was a physicist. Who better to trust than a physicist?

Her heart pounded just thinking about it. This was real. It was time to get serious. “Maybe you could explain it to me,” she said. “In baby words.” Maybe if she understood it better, she’d be better equipped to fight the knot of fear that never left her stomach when she thought about her mom disappearing into space and time.

Mom looked pleased. Ellie had never asked for a detailed explanation before now. For starters, science wasn’t her thing. Actually, school wasn’t her thing. She was way more comfortable in the gym than in a lab. Ellie sometimes wished she were a better student. She was probably a disappointment to her mom.

“Well,” Mom began, “the flow of time, the hours and days and years, is cognitive. It’s made up by our brains. That means time travel could have a direct connection with neural activity in the brain.”

“So time travel is just made up? It’s not real?” Ellie asked.

“What do you mean by real?” her mom argued. “How do you know right now is real?”

“It just . . . feels real.”

“Time travel would feel the same.”

“Yeah. It totally did,” Ellie admitted.

Mom pointed proudly. “The gizmo is primarily electrical,” she said. “It manages the cognitive and tactile sequences that convert the physical to the neurotemporal. That is, the sequences that allow a body to displace within a timeline.” She frowned. “But there are a few things left to fine-tune.”

Ellie was already lost. “Like . . . ?”

“Like I’m not certain what factors combine to launch the thing. And I’m wondering why you traveled for that length of time. There’s a theory that you can’t travel to a time where you already exist.” Mom looked at her daughter in awe. “Ellie, you probably just proved that theory! That must be why your trip failed.” She wrapped her arms around Ellie and squeezed.

Ellie gasped and broke free. “So let me get this straight. You don’t know how to turn it on. You don’t know how to set it for a specific time. And you aren’t sure you could get back home. In other words, I’m just lucky I didn’t land on some other planet five hundred years ago?”

“Hmm, yes, sort of. But think of the neuro sequencing as fuel. I don’t think a traveler can produce enough of it to go five hundred years. And you can’t go just anywhere. The positioning coordinates are limited to Earth.” She sighed, then frowned. “I’m so, so close. I’d give anything to know why it sent you and not me, what you did or said or thought to trigger it, why—”

“The trigger?” Ellie interrupted. “Mom. It was a clam.”

Mom frowned and grabbed her laptop. “That’s impossible,” she said, tapping away and talking to herself. “Although salinity could be a factor. Or maybe mineral levels? Selenium, zinc, iron . . . iron’s magnetic, but not enough. I could test it . . . I’m going to need a bigger mollusk.” She slammed the laptop closed and put her face in her hands. “What am I doing?” she whispered.

“Couldn’t you work on a less dangerous invention?” Ellie asked gently. “Maybe one with kittens? Or life jackets?”

Mom looked ready to cry as she picked up the gizmo and turned it over in her hands, but her voice was firm. “Ellie, you know I have to do this.”

Ellie didn’t understand. Other kids didn’t have to worry about their parent getting lost in time and never coming back. One look at her mom’s set jaw told her not to argue. But she couldn’t help asking, “Can you just promise you won’t take any chances until you figure everything out?”

“I promise! As much as I can,” Mom said, crossing her fingers over her heart.

That would have to do.

Mom opened her laptop again. “Meanwhile, it’s probably best if you stay out of the lab when I’m not here.”

“Not a problem,” said Ellie, heading for the stairs. “And I’m throwing out the linguini!” She stopped on the stairs and turned around, remembering something. “Hey, Mom—I never did tell you what was in my birthday card.”

“I think I know,” said Mom, back to tapping at the keyboard. “Your dad phoned yesterday, at the last minute as usual. He and Kat will be here in the morning.”

Great, thought Ellie. As if things weren’t complicated enough already.

4

Ellie woke up the next morning with way too much on her mind. Yesterday, she’d accidentally become maybe the first person in the history of the world to travel through time, even if the trip was only a few seconds long. And it wasn’t like she could tell anyone. Maybe one day she’d be famous, if her mom actually . . . She couldn’t bear to think about that, so instead she thought about something less scary. Today she was twelve!

She rolled out of bed, wondering if Kat would be different this year. Ellie sometimes wished they were growing up together the way identical twins are supposed to. They barely knew each other. And this visit was bad timing. School was about to start. The twins’ August birthday meant Ellie was one of the oldest kids in her class. She’d waited forever for middle school! No way she was skipping a day just because Kat was here.

She stood in front of her closet and tried to push away the possibility that she simply didn’t like her sister. Kat was an oddball, always with her nose in a book or her phone. Last year, she’d told Ellie she wanted to be an “information retrieval specialist” when she grew up. When Ellie didn’t reply, Kat explained, “It’s for fact-checking. I’m taking a coding class. Coding’s essential to information architecture.” Ellie didn’t have a clue what that meant. Ellie didn’t even have a phone. To her, it just sounded like Kat was showing off.

Kat wore skirts and dresses. Ellie usually threw on leggings. Did she even have a skirt? She dove to the back of her closet and found one. It was long and looked funny on her sturdy, muscled frame. She found a cotton shirt that buttoned and a funky short vest printed with geometry equations her mom had given her. Overall it was a nerdy kind of Little House on the Prairie look. Kat would love it. Ellie put on some fuzzy wool socks and short boots.

Downstairs, her mom was drinking coffee and looking at her tablet. Mom got up to give Ellie a hug. “Happy birthday, sweetheart,” she said, kissing the top of her head. She looked at Ellie’s outfit and raised an eyebrow. “Dressing to impress?”

“Kind of,” Ellie admitted. “It’s my librarian look.” She spied a small package tied with a bow on the table. “Ooh! Is that for me?” she cried. “Is it a phone? You got me a phone?”

“Go ahead and open it,” laughed her mom.

Tearing open the box, Ellie jumped up and down with delight. The phone was small and silver with a rugged turquoise military-grade protective case. “It’s limited,” Mom warned. “I already set up the parental controls.”

Ellie didn’t care. “It’s perfect!” she squealed. “And look at this case—I could drop it off a roof!” Ellie rushed to give her mom a huge hug. “Thanks, Mom. You’re the best.” She plugged in the phone to charge and looked hopefully toward the stove. “Anything special for breakfast?” Between gymnastics, aikido, and parkour, Ellie was pretty much always hungry. Her mom wasn’t much of a cook, but birthdays were birthdays, and she’d already been to the bakery. Over a plate of Ellie’s favorite chocolate croissants and morning rolls, they talked about the plan for the day.

“How long is Kat staying? School starts Tuesday.”

Mom hesitated. “I really meant to talk to you about this last night, but then we got sidetracked . . .”

“What?” Ellie’s heart sank. She and her friends had been talking for a year about entering middle school. “I’m not missing the first day!” she said. “If I have to, I’ll take Kat with me.”

“That’s the thing,” said Mom. “Kat’s going to stay. She’s going to live with us this year. She’ll be going to school with you every day.”

5

Ellie sat, stunned, while her mother explained how she and Michael thought Kat was now at an age where she needed more stability. Her education had been scattershot, mostly online and with random tutors. She didn’t have any friends her own age, girls or boys. The cabarets and theaters Michael acted in weren’t exactly the best atmosphere for raising a young person.

“Why didn’t you tell me?” Ellie demanded. “Where will she sleep? Will she be in all my classes?”

“Calm down,” said Mom, her voice firm. “I’m as surprised as you are. Your father and I talked this over for the first time yesterday. I offered to take Kat, and he accepted. We can get bunk beds for your room. We can redecorate! You can pick the paint. And I don’t know about classes, but we can probably request that you be together—or not.” Mom frowned. “I know it’s a lot to absorb, and I’m sorry for the timing. But can you at least understand why it’s necessary?”

“Not really.” Everyone always said travel was the best education. Surely it was better than sixth grade at Rennart Middle School. Having Kat here would be like growing a third leg. A leg that wanted to walk in a different direction. A leg that probably thought you were stupid. A leg that—

“Ellie.” Her mom was waiting for a reply. “They’ll be here any minute.”

There was no point arguing. “Whatever. And what about the Thing in the Basement? Are we sharing that with Kat?”

Her mom frowned into her coffee. “Yes,” she said. “As soon as possible. She deserves to know what’s going on. But it’s a bit much to throw at her right away.” She reached out to put an arm around Ellie’s shoulders, but Ellie shrank away, not wanting comfort. She wanted to be mad. Her mom went on. “Try to see this as a chance to finally get to know Kat. You have an identical twin! Do you know how precious that is? If you make this effort, I promise you’ll never be sorry.”

Ellie knew her mom was right in theory, but it seemed hopeless when she and her sister were so different. What her mom hadn’t said but Ellie knew she was thinking was “And she’ll be a good influence on you.” Kat didn’t waste her time hanging around gyms and dojos; she’d be great in a science lab. She’d probably be all over Mom’s work, helping her with computer coding and “information retrieval.”

Still, by the time the doorbell rang twenty minutes later, Ellie was finished being a brat and ready to try a little. Maybe a miracle would happen. Maybe by tonight they’d be whispering and giggling and sharing their deepest secrets. She opened the door, and there was her beaming dad, tall, dark, and movie-star handsome. Behind him, slumped over a phone looking bored, was Kat. In skinny black pants and a black T-shirt, wide studded leather bands around both wrists. Her hair was jammed into a tight cap, but a curl of purple dangled across one eye. To complete the look, a silver ring pierced her nose.

Michael stood aside and nudged his daughter with an elbow. “Say hi, Kat,” he prompted.

Kat sighed and glanced up at Ellie and Mom without smiling. “Hey,” she said, and went back to her phone.