WHEN DAK saw Sera emerge from behind the sculpture-covered stone wall, he had to cover his mouth with a fist to stifle a laugh.

“What?” Sera said.

“Nothing,” Dak told her, launching into a fit of fake coughing.

She was dressed in a crazy-looking sack with a hole cut out for her head, as well as a long, colorful skirt that dragged in the dirt behind her when she walked. But the weirdest part was how closely she resembled one of them. The Mayas. Same skin color and high cheekbones. Same coarse, dark hair. If Sera wanted, she could probably pass for a local.

Now was not the time to bring it up, of course. They’d just downloaded a seemingly impossible riddle on the SQuare. And Dak had been best friends with Sera long enough to know when not to mess with her.

“Go on, Dak,” Sera said.

“I promise,” he told her. “It’s nothing.”

“Say it!” she demanded.

The look on her face told him she wasn’t going to drop it. “Okay, fine,” he said. “I was just thinking about . . . um, how nice of an outfit that is.”

“Like your loincloth is any better?” Sera said, pointing below his waist.

“It’s not a loincloth,” Dak said, instinctively covering himself. “It’s a breechcloth.” He looked down at the clothes Riq had swiped for him off of a tree near a cluster of empty huts. “And maybe your vision’s been compromised from all that crying you were doing back there, but I’m also clearly wearing pants —”

“More like leggings,” Sera said.

Dak turned to Riq for help. He was wearing the exact same outfit. But Riq was too busy peeking out from under the overhang that was keeping them out of the rain, watching the Mayas continuing to hurry past.

Dak sighed.

Sometimes it got lonely trying to rescue history all by himself.

“Can I see the riddle one more time?” Riq asked, turning back to the others.

Sera handed over the SQuare, and the three of them studied the nonsensical words for the tenth time:

A snake charmer and a clown

A treasure that never was

A gift from the deity Itzamna: from 9.10.5.10.7 to 11.17.2.13.10

Trace the symbol of the ceiba tree toward the truth of the curse

Dak threw his hands in the air. “Impossible!” He didn’t have the first idea how to approach it. And usually he was pretty good at working through the cryptic clues the Hystorians had left so they’d know which Break to fix.

“We have to make a decision,” Riq said, looking up at Dak and Sera. “We either search for a better place to wait out this rain, or we ignore it and concentrate on solving the riddle.”

“It’s not even a question,” Sera said. “We have to figure out where we should be and what we should be doing.”

“You think you can do it in these conditions?” Riq asked.

“I know I can. We’ve cracked number ciphers before.”

“Then let’s get to work.”

“Uh, guys?” Dak said. “Excuse me?” When they’d both turned to face him, he said, “Don’t you think I should maybe have some say in this, too?”

“What is it, Dak?” Sera asked.

“Well, it’s been awhile since we’ve eaten, right? I mean, technically it’s been several hundred years.”

Sera rolled her eyes. “And your point is?”

Dak motioned to Riq. “What do you say we send this guy off to find us a nice cheese plate? I’m thinking Gruyère and cheddar. Maybe a few figs and grapes on the side. Oh, and saltines.”

Sera’s mouth fell open. “Are you kidding me right now, Dak?”

“Fine, nix the saltines,” Dak said. “I get it: You’re in the mood for something a bit classier. Let’s go ahead and spring for TriSQuits, then.”

“An absolute child,” Riq said, shaking his head.

Sera and Riq both turned away from Dak and began tinkering with the SQuare. “Seriously, though,” Dak called to them, “aren’t you guys hungry?”

They ignored him.

Dak watched them work for a few minutes. Sera obviously knew what she was doing. She was a genius when it came to science, so working with numbers came somewhat naturally to her. And as a language whiz, Riq had an advantage over Dak whenever their clues involved codes or ciphers. Knowing that didn’t make it any easier to be benched, though.

“Whatever,” Dak muttered under his breath.

He wandered a few yards down the stone wall and sat against it, watching the rain and thinking about the riddle. A snake charmer. A clown. A treasure that never was. The truth of the curse. None of it rang any bells.

Being left alone like this reminded Dak of what got them into this history-saving situation in the first place. Just a few days ago — Wait, how was he supposed to measure days while traveling through time? He couldn’t exactly consult a modern calendar. And the Mayan version wouldn’t do him any good.

However long ago it was, the last time they were back home, in the present, he’d mistakenly let Sera into his parents’ lab, where she had become obsessed with the Infinity Ring, ignoring him for hours and hours and hours — just like she was ignoring him now. Dak shook his head, thinking about that fateful day. If he’d never shown her what his parents were working on, Sera never would’ve figured out the missing piece of the puzzle. And if she hadn’t figured out the missing piece of the puzzle, they never would’ve taken that stupid test run back to the Revolutionary War, and his parents wouldn’t be lost somewhere in time right now.

Dak watched several more Mayas race down the white street, carrying their children in their arms. It was a strange sight considering the rain was hardly more than a lazy drizzle, though the wind was definitely picking up now.

Dak leaned his head back against the wall, fingering the iron key he had tucked into the side of his leggings. His parents had given it to him in the year 911, somehow knowing that he would need it to escape the SQ in 1850. It boggled his mind.

Dak squeezed his eyes shut, tightened his grip on the key, and imagined their faces. He understood that what he, Sera, and Riq were doing was monumentally important. They were literally trying to save the world. And he loved warping back to different parts of history, seeing famous events unfold right before his eyes. But lately, in secret, Dak wondered if he wouldn’t ditch all the heroics in exchange for having his mom and dad back in his life — even for a day.

These thoughts made Dak feel guilty, so he got up and hustled back over to Sera and Riq, saying, “Never fear, my fellow time-traveling comrades, I’ve come to save the day. Please, how might my talents best be utilized?”

They didn’t even acknowledge his existence.

“Guys?”

Nothing.

Dak shrugged. If they didn’t need him, he didn’t need them either.

He turned to go and explore the wet Mayan village on his own. If he was lucky, he’d find some vital clue to the riddle . . . which he wouldn’t share with anyone.

Dak found himself crossing back over the white road, toward a large domed building a little ways off. It looked like an observatory. He cupped a hand against his forehead to keep the rain out of his eyes. It was so hot and humid he was almost thankful to be wearing a breechcloth. It was actually keeping him fairly cool and allowed for occasional drafts that proved tremendously refreshing. What if he started rocking one of these bad boys in the present? Would it catch on? He pictured all his bros in fifth grade wearing them, too. Sitting around the caf, talking. Lining up for assemblies. Eventually they’d run a nice profile piece on him in the school paper next to the caption Dak Smyth, more than your ordinary history genius.

Then he remembered one very important fact:

He didn’t really have any bros.

Unless he counted Sera — which he decided he did.

Dak tried all the doors of the observatory, but they were locked. He was surprised by the size of the building. According to his research on Mesoamerican civilizations, the Maya were curious about astrology. And art. And music. But they didn’t have the technology for anything overly refined — for instance, they probably weren’t spreading their cheese onto TriSQuits.

Thunder crashed so loud overhead, Dak flinched. The rain started falling harder, too, and at an odd angle.

Dak knew he should hurry back to the others, get out of the brewing storm, but just then he spotted a narrow opening in the observatory wall, like a small glassless window. He moved toward it and peered inside, the rain raking down his back. It was dark inside, except for a few candles that burned near the far wall of the large room. Next to this wall, which had a large painting of a tree, were three older men kneeling on the floor, writing on a massive sheet of a paper-like material. The thing was longer than they were tall.

Then, on the floor beside them, Dak spotted something else. A colorful mask. The kind a clown might wear. Dak immediately thought of the riddle. Maybe there was some kind of connection. And then Dak considered something else. Something potentially incredible. What if these men were working on the Great Mayan Codex? He knew there were probably many codices, a type of book, produced during this era. But his heart sped up anyway. Because everything around him made him think he was in the seventh century. And that meant it was possible that he was witnessing the composition of one of the most revered texts in all of history.

Dak pounded on the wall, so excited he was having trouble breathing. As soon as the men looked up, though, he thought better of it and ducked out of sight. Because if the authors of the Great Mayan Codex had prophesized that the SQ would one day come along and save all mankind, it was possible that the authors themselves were SQ. Or even a group of Time Wardens, whom the SQ had positioned throughout history to protect their agenda from meddling time travelers . . . like Dak.

He crouched there for several long minutes, trying to think.

Rain pummeled his entire body, puddling around his knees and elbows.

He finally pushed away from the observatory and sprinted back across the road. He had to go tell Riq and Sera about the clown mask. And the codex. Even if they didn’t deserve to know.

When Dak finally rounded the stone wall and spotted his friends, he stopped in his tracks. “No,” he said under his breath.

Riq and Sera were surrounded by three thuggish-looking Mayas, one of whom was holding the Infinity Ring in his grimy hands.