Amy, Atticus, and Jake ran and jumped back onto the circling belt behind a big box that hadn't been claimed. One of the men grabbed Atticus's arm and yanked him off.

"Let go!" Jake jumped up, kicking the man swiftly in the chest. The man reeled, knocking the soldier behind him over. They stumbled, tripping over luggage and landing in a heap on the floor.

Amy ducked as a rubber mat swept over their heads, knocking Att's gla.s.ses askew. Dan waited for them on the other side as they were dumped out into a secure luggage area and tumbled down a ramp. It was like streaking down a very lumpy slide. Airport workers stared at them in shock and then erupted into a clamor of angry Spanish.

"Don't worry, dudes, we're out of here," Dan said.

Amy glanced back. One of Pierce's men came through the flap, but an airport security guard dragged him back. Security couldn't hold him for long, she knew. "Gate Seven. Move it," she told the others.

They ran past carts piled with luggage, out onto the tarmac. Six of Pierce's men emerged from the luggage area, scanned the tarmac, and pointed in their direction. "Where's our chopper?" Jake asked Amy.

Amy nodded at a helicopter revving up on the tarmac. "That's it up ahead."

"We're not going to make it!" Atticus cried.

Atticus was right. Pierce's thugs had taken a small dose of the serum, and their super-enhanced bodies could run faster than the kids ever could. Without that chemical advantage, the kids had no chance in a flat-out race.

Amy and the others charged for the chopper, but she could feel the men closing in, a hundred yards behind her, fifty, twenty . . . their footsteps pounding, louder and louder, each step sounding of doom.

Amy could almost feel the soldiers' hot breath on her neck - it had a certain odor, a kind of green kale smell mixed with chlorine and ammonia. She knew that smell all too well by now, from far too many run-ins with brick-like men who were trying to kill her.

She turned, preparing to fight. There were five men, four kids . . . outmanned and out-muscled, but if they were smart they might have a chance at escape. She spotted two airport mechanics inspecting a plane about a hundred feet away. Maybe if she could get their attention, the soldiers would be afraid to attack.

She jumped up, waving and shouting, "Hey!" as one of Pierce's men leaped for her. She ducked and let him sail over her, landing with a thud on the runway. Just then a loaded luggage truck zoomed out of the terminal, heading for a jet waiting on the tarmac.

"Jump on!" Amy shouted. She leaped onto the truck as it pa.s.sed, hiding behind the mountain of suitcases. She reached for Atticus's hand to haul him up after her, but it was slick with sweat and slipped through her fingers. He ran, panting, to keep up with the racing truck. She grabbed hold of his wrist this time and yanked him up so hard she nearly dislocated his shoulder.

Jake and Dan hauled themselves over the side at the last second.

Amy looked back to see how much ground they'd gained, but Pierce's men kept coming, not far behind the speeding truck. They had no time to spare. She waved frantically at the pilot of their helicopter, who was sitting at the controls. "Let's go!" she shouted at him. "Now!"

The chopper motor roared to life, and the rotors began to turn, slowly at first, then faster. The driver popped open the door.

"Jump!" Amy called to Jake, Dan, and Atticus. "Now!" She took Att's hand as they hopped off the speeding luggage truck. Amy landed on her knees and rolled over the hot tarmac. She pulled Atticus to his feet and ran for the chopper, Jake and Dan right behind them. Pierce's men were closing in. Amy and Dan scrambled aboard the helicopter. Jake pushed Atticus on, jumped in, and shut the door as the rotors whirred faster and the chopper lifted off.

The pilot yelled something at them in Spanish, and Jake yelled something back at him. "He's asking why those big men are chasing four kids," Jake translated. "I told him to just get us out of here." The pilot bellowed again, pointing at the tarmac just below. One of the thugs was leaping into the air, freakishly high, trying to grab the landing skid. He barely missed, tumbling to the ground unhurt as the chopper rose out of his reach.

Amy breathed a quick sigh of relief.

"Thank goodness goons can't fly," Dan said. "Not even serum-enhanced goons."

The boys settled into their seats behind the pilot and buckled up for the ride to Tikal. It was a big helicopter with two rows of three seats facing each other behind an enclosed two-seat c.o.c.kpit. Amy poked her head into the c.o.c.kpit to make sure the pilot knew where they were going and to thank him for his quick thinking.

"My pleasure," he said in a thick accent, nodding but not meeting her eye. "Please sit down and buckle your seat belt, miss. The ride to Tikal can be b.u.mpy. We'll be flying over active volcanoes."

Amy sat down and buckled up. Something was bothering her; something about the pilot didn't look right. His torso was thick and lumpy under his jacket. "Did you notice anything strange about the pilot?" she whispered to Dan.

"Like what?" he asked coldly, as if it took superhuman effort just to respond to her.

"Never mind." Amy pressed her forehead against the window, frustrated.

The helicopter rose and left Guatemala City behind. Far below, a blanket of brown volcanic mountains rippled.

She shifted her leather bag to the floor and heard a tiny clink. She couldn't resist another glance at Dan, who was now engrossed in a computer game. His straight brown hair fell into his eyes, and he had to keep reaching up to sweep it out of his way. Amy tried to stifle a surge of tenderness for him, but the sight was enough to make her heart sting like skin recovering from frostbite. It sometimes was easy to forget that he was only thirteen. If they were still in Attleboro, the biggest thing they'd be fighting about would be haircuts and homework, arguments she'd likely lose because Dan was the most stubborn person she'd ever met.

No wonder they were barely speaking to each other.

Dan was sick of the whole Cahill thing. "I'm out," he'd told her. Once they finally took down Pierce, no more Cahill stuff for him. He planned to disappear and live out the rest of his life quietly and anonymously, with as little mystery, action, and adventure as he could manage.

Amy remembered a time, not so long ago, when Dan would have dismissed a life like that as boring. That's the kind of damage the Clue hunt had done to him. A boy whose life had been so stressful he was ready to retire at thirteen.

Atticus sat next to Dan, his wiry body curled in his seat, poring over Olivia's Codex, his older brother, Jake, beside him, reading over his shoulder. He'd been fixated on a page of weird, unfamiliar glyphs that he couldn't figure out. They were lined up in neat rows, each one a rounded square with a design inside, and between each one was a set of letters and numbers. Amy had looked at the symbols but couldn't make much of them. Sometimes she saw something that looked like a face or a tongue or a monster. Sometimes they were just dots and lines and circles, almost decorative. They were complex shapes, not letters, exactly, but almost like rough drawings . . . though of what?

They had left the seat next to Amy empty. No one wanted to sit next to her. Jake least of all. Her heart cramped as the ghost of her cruel lie echoed in her head. I don't love you. . . . You think there's this thing between us, but there never was, and there never will be.

They didn't understand what it was like, being in charge. They didn't know how it felt to send someone you love off on a mission so dangerous that death was nearly certain. She refused to be the reason her little brother never got another haircut. One more mishap, and she'd be staring at his s.h.a.ggy brown hair against the lining of a casket. From now on, she'd do what was necessary to keep her family - and the world - safe from Pierce.

If that makes them angry, then too bad. She'd rather have them angry and alive than dead. She put her backpack under her seat and heard the clink again. It had been made by a small flask of Cahill serum. No one knew she had it. She hated the idea of having a full, undiluted dose of the serum near her. It was like keeping something radioactive next to your skin, like Superman carrying around Kryptonite.

Atticus was working on decoding the formula from Olivia Cahill's Codex. Lately he'd been obsessed with a recipe in the book for "Crystal Sugar Candy." "If you want some candy so badly, Atticus, I'll buy you some when we land," Amy joked, mostly to try to jolt one of them into acknowledging her presence.

"It's not that," Atticus said. "Rock crystal candy is very simple to make. This recipe is ridiculously complicated. There's something else going on here."

"Crystal . . ." Amy mused. "Maybe there's a connection to riven crystal."

"Maybe," Dan said. "But what is riven crystal?"

"Read the description again, Jake," Amy said.

Atticus handed the Codex to Jake. Olivia's description of the crystal was written in Latin, and Amy's Latin was poor-to-nonexistent.

Amy's phone buzzed. "Finally," she said with relief. They'd been out of cell range and out of touch with their base in Attleboro for several hours, and it made her nervous. "It's Ian. Hang on a sec, Jake."

She could sense Jake stiffening from across the aisle and caught the annoyance - or was it anger? - that flashed across his face.

"Ian?"

"Amy."

"It's good to hear your voice."

"Yes, we've been trying to reach you since you left US airs.p.a.ce," Ian said. "Did you make the chopper we set up for you?"

"Yes." No point in going into how they'd barely made it out of the airport alive. "Thanks for your help, Ian."

Out of the corner of her eye she could swear she saw Jake wrinkle his nose and mutter, "Thanks for your help, Ian" under his breath. Typical. Jake could barely look at her without grimacing, yet watching her talk to a boy she'd once had a crush on turned him from dark and brooding into p.r.i.c.kly and childish.

"How's Ian?" Jake asked when she got off the phone. He straightened his spine, b.u.t.toning the top b.u.t.ton of his shirt and sticking his nose into the air. "Tip-top shape, I hope?" he added in a terrible, exaggerated British accent. "All's jolly well in old Attleboro, is it? Or as I call it, Yankee Purgatory? I do hope I'll be able to leave this blasted land of rubes and return to civilization one of these days."

Dan and Atticus snickered in their seats. Amy crossed her arms, annoyed. "Just read me Olivia's description of the ingredient, please."

"I say, it says here that she used flakes of a riven crystal chipped off a stone from a Mayan temple in Tikal." Jake was still using his fake Ian accent.

"Thank you. You can drop the accent now."

"Jolly good. Funny, I thought you liked British accents."

"Jake -"

"My mistake."

"Yes. It is your mistake. What else does Olivia say? In your regular accent, please."

Jake frowned at the book. "Basically, Olivia looked at the rock under a magnifying gla.s.s and saw that its crystals had an unusual zigzag structure, as if it had been deformed by some great pressure."

"That sounds like shocked quartz. I saw it on Weird But True," Dan said. "It's found in places where nuclear devices have been set off, but also in places where a meteor crashed to earth."

"Chicxulub!" Atticus said.

"Gesundheit," Dan said back.

"No, the Chicxulub crater," Atticus continued. "A meteor hit the earth there about sixty-five million years ago. It caused giant tsunamis and sent up so much dust it almost caused an artificial ice age - like a nuclear winter. Some scientists think that meteor is responsible for the extinction of the dinosaurs."

"I'm a fan of the volcanic theory myself," Dan chimed. "That volcano dust wiped them out."

"Whatever, a meteor landed there," Atticus said. "They've found shocked quartz in that spot, deformed by the impact of the meteor. But it's in the Yucatan, in Mexico, not in Guatemala."

"The Maya traded all over Central America," Jake said. "They could easily have traded for stones from the Yucatan."

"If all we need is a piece of shocked quartz, we can buy it off the Internet," Dan said. "We don't need to fly all the way to Guatemala."

"The book specifically calls for a 'riven crystal from Tikal,' " Jake said. "It must have some special properties."

"Did the Maya build temples out of it?" Dan asked.

"I checked into that," Amy replied. She was grateful that, at least when they were discussing the antidote, the others dropped the silent treatment. "The temples are built of local limestone. But they might have put special stones at the altars of the temples, maybe something they traded for, something unique."

Tikal was a national park and archaeological treasure. The ruins of a great ancient city - a fallen empire - had been hidden by centuries of jungle growth, but in 1956 archaeologists began to excavate and were amazed at what they found: whole cities made of stone, huge Mayan pyramids and temples, miles and miles of ancient buildings.

"Just as I thought," Atticus announced, waving the paper he'd been using to decode the candy recipe.

"It won't make candy?" Dan asked.

"Not unless you like candy so hard it will break your teeth," Atticus said. "It's a coded message. Sugar, or sucrose, has a chemical formula of C12H22O11, but when I decoded this ingredient list, the formula for 'sugar' reads SiO2. That's the chemical formula for quartz. But it goes on to describe a molecular structure that's a little off, not quite right for quartz. Once I applied the molecular structure for riven quartz to the code, I figured it out. The antidote requires a special piece of riven rock, which has certain molecular properties. One of those special pieces is embedded in the ruins of a Mayan temple in Tikal. The piece Olivia used was broken off from that crystal."

"But Tikal is full of ruined temples," Amy said.

"And it's gigantic," Jake added. "How will we know which temple holds the crystal we need?"

"Let me have the book back, Jake," Atticus said. He opened it to the page covered with weird glyphs.

"Check it out." Dan nodded at the window. "That volcano is spewing ash."

Just then the chopper blew through a brief black cloud. Everything went dark outside the windows. For a second, Amy had the feeling she was suffocating. But the black cloud - the ash Dan had just been talking about - disappeared quickly.

The chopper swerved to the right, then veered sharply to the left. It lurched up and down.

"What's going on?" Jake asked.

Another lurch, and Amy felt her stomach drop to her knees.

"Whoa!" Atticus shouted.

"This is better than a roller coaster!" Dan said.

"This isn't good." They were far from Guatemala City now, flying over mountains and jungle that looked like the middle of nowhere. Amy opened the part.i.tion dividing the c.o.c.kpit from the pa.s.senger seats and caught the pilot quickly sitting down.

"What's going on?" she asked.

The pilot didn't look at her. "No English."

No English? Hadn't he told her to sit down and buckle her seat belt? She noticed his coat on the seat next to him. She leaned farther into the c.o.c.kpit and immediately realized why the pilot had looked like he had a lump under his coat. He had a parachute strapped to his back.

A wave of anxious nausea washed over Amy. "What do you think you're doing?" she demanded. The pilot refused to meet her eye. The chopper lurched again, just missing the side of a mountain.

"He's wearing a parachute!" she told the others. "I think he's going to jump!"

"Pierce must have gotten to him," Dan said.

The pilot jerked on the handle of the c.o.c.kpit door to his left, trying to open it and throw himself out. "Grab him!" Jake shouted.

Amy ducked out of the way. Jake dove through the part.i.tion and grabbed the pilot before he could open the outside door. "Dan, help me!"

Dan reached through the part.i.tion door and helped Jake drag the pilot into the pa.s.senger area. The chopper immediately began to drop.

"Amy - take the controls!" Jake barked.

Amy crawled over Dan and Jake, who were wrestling the pilot, into the front seat and grabbed the controls. She panicked. Now what?

"Steady this thing!" Jake shouted.

"How?" Amy shrieked back at him.

"I don't know!" Jake called back.

The chopper nosed down toward the trees. She pulled on the control stick in front of her and the nose tilted up. The chopper didn't rise, but it stopped falling. It leveled and moved forward - straight for the side of a volcano.

"AMY!" Dan screamed.