ONCE THEY GOT out of camp, the Fifth Cohort formed two lines behind the centurions, Dakota, and Gwen, who had accepted Brooklyn into the cohort. They marched north, skirting the edge of the city, and headed to a nearby field. The grass was cropped short. The earth was pitted with explosion craters and scarred with trenches. At the north end of the field stood the target. There was a stone fortress with an iron portcullis, guard towers, scorpion ballistae, water cannons, and probably more fun surprises.

"They did a good job today," Hazel noted. "That's bad for us."

"Wait," Brooklyn said. "You're telling me that fortress was built today?"

Hazel grinned. "Legionnaires are trained to build. If we had to, we could break down the entire camp and rebuild it somewhere else. Take maybe three or four days, but we could do it."

"Let's not," Percy said. "So you attack a different fort every night?"

"Not every night," Frank said. "We have different training exercises. Sometimes death ball — um, which is like paintball, except with . . . you know, poison and acid and fire balls. Sometimes we do chariots and gladiator competitions, sometimes war games."

"I like paintball," Brooklyn offered, absentmindedly spinning her ring. "I have a paintball gun attached to this ring, along with my club. It's fun."

Hazel pointed at the fort. "Somewhere inside, the First and Second Cohorts are keeping their banners. Our job is to get inside and capture them without getting slaughtered. We do that, we win."

Percy's eyes lit up. "Like capture-the-flag. I think I like capture-the-flag."

Frank laughed. "Yeah, well . . . it's harder than it sounds. We have to get past those scorpions and water cannons on the walls, fight through the inside of the fortress, find the banners, and defeat the guards, all while protecting our own banners and troops from capture. And our cohort is in competition with the other two attacking cohorts. We sort of work together, but not really. The cohort that captures the banners gets all the glory."

Percy stumbled, trying to keep time with the left-right marching rhythm. Brooklyn laughed at him.

"How are you doing this?" he asked her.

"I'm just better," she replied.

"Shut up," he told her.

She smirked. "So why are we practicing this, anyway?" she asked. "Do you guys spend a lot of time laying siege to fortified cities?"

"Teamwork," Hazel said. "Quick thinking. Tactics. Battle skills. You'd be surprised what you can learn in the war games."

"Like who will stab you in the back," Frank said.

"Especially that," Hazel agreed.

They marched to the center of the field and lined up. The other two assembled as far as possible from the Fifth. The centurions for the attacking side gathered for a conference. In the sky above them, Reyna circled on her pegasus.

Half a dozen giant eagles flew in formation behind her. The only person not participating in the game was Nico di Angelo, who had climbed an observation tower about a hundred yards from the fort and would be watching with binoculars.

Brooklyn gingerly put on the armor, grimacing because of how it felt against her dress and her gloves. She didn't mind the cold, but come on, why'd they have to put her in a dress? Nonetheless, she strapped it on, nearly getting it done when she reached for another strap and winced. Her arm hurt. Why did it hurt?

Her mind offered up a memory: one of those red lines that she could see when she became smoky was starting to tear apart, her body leaping at the red line, the feeling of a knife stabbing into her shoulder . . . the blood . . . the phantom pain that came with it.

Her vision swam. Her head throbbed at the memory, and so did her arm. When she could see again, her vision clear, Frank was saying something to Percy.

"You did it right," Frank said in amazement. "Percy, you must've done war games before."

"I don't know. Maybe." Percy took out his sword and leaned on it, looking over at Brooklyn. "Are you good?"

"Can you get the one in the back for me?" she turned around, and instantly he gave her his sword to hold, his fingers moving to help her out. "My arm hurts."

"Your arm?" she didn't miss the concern in his voice.

"I don't know. I think it's a phantom pain."

"From what?" he finished strapping the armor, so she turned and gave him his sword back.

"I'll tell you later," she spun her ring a certain way, and her club appeared, fitting perfectly in her hands.

He was looking at her dubiously, but she focused on Frank, who was also frowning at her. "We can use real weapons, right?" she asked him.

"Yeah," Frank agreed. "For sure. I've just never seen a sword like that. Or a club like that."

"What if I hurt somebody?" Percy asked.

"We heal them," Frank said. "Or try to. The legion medics are pretty good with ambrosia and nectar, and unicorn draught."

"No one dies," Hazel said. "Well, not usually. And if they do—"

Frank imitated the voice of Vitellius: "They're wimps! Back in my day, we died all the time, and we liked it!"

Hazel laughed. "Just stay with us, guys. Chances are we'll get the worst duty and get eliminated early. They'll throw us at the walls first to soften up the defenses. Then the Third and Fourth Cohorts will march in and get the honors, if they can even breach the fort."

Horns blew. Dakota and Gwen walked back from the officers' conference, looking grim.

"All right, here's the plan!" Dakota took a quick swig of Kool-Aid from a flask. "They're throwing us at the walls first to soften up the defenses."

The whole cohort groaned.

"I know, I know," Gwen said. "But maybe this time we'll have some luck!"

The campers grumbled and complained. Apparently this happened a lot. Which was why Brooklyn should be the one to break it. She's the epitome of luck, after all.

"First line with Dakota," Gwen said. "Lock shields and advance in turtle formation to the main gates. Try to stay in one piece. Draw their fire. Second line—" Gwen turned to Brooklyn's row without much enthusiasm. "You seventeen, from Bobby over, take charge of the elephant and the scaling ladders. Try a flanking attack on the western wall. Maybe we can spread the defenders too thin. Frank, Hazel, Brooks, Percy . . . well, just do whatever. Show Brooks and Percy the ropes. Try to keep them alive." She turned back to the whole cohort. "If anybody gets over the wall first, I'll make sure you get the Mural Crown. Victory for the Fifth!"

The cohort cheered half heartedly and broke ranks.

Percy frowned. "'Do whatever?'"

"Yeah," Hazel sighed. "Big vote of confidence."

"What's the Mural Crown?" Brooklyn asked.

"Military medal," Frank said. "Big honor for the first soldier to breach an enemy fort. You'll notice nobody in the Fifth is wearing one. Usually we don't even get into the fort because we're burning or drowning or . . ."

He faltered, and looked at Percy. "Water cannons."

"What?" Percy asked.

"The cannons on the walls," Frank said, "they draw water from the aqueduct. There's a pump system — heck, I don't know how they work, but they're under a lot of pressure. If you could control them, like you controlled the river—"

"Frank!" Hazel beamed. "That's brilliant!"

Percy didn't look so sure. "I don't know how I did that at the river. I'm not sure I can control the cannons from this far away."

"We'll get you closer." Frank pointed to the eastern wall of the fort. "That's where the defense will be weakest. They'll never take four kids seriously, even if Brooks is one of them," he added quickly, making her beam. "I think we can sneak up pretty close before they see us."

"Sneak up how?" she asked.

Frank turned to Hazel. "Can you do that thing again?"

She punched him in the chest. "You said you wouldn't tell anybody!"

Frank's face fell.

Hazel muttered under her breath. "Never mind. It's fine. Brooks, he's talking about the trenches. The Field of Mars is riddled with tunnels from over the years. Some are collapsed, or buried deep, but a lot of them are still passable. I'm pretty good at finding them and using them. I can even collapse them if I have to."

"Like you did with the gorgons," Brooklyn said, "to slow them down."

Frank nodded approvingly. "I told you Pluto was cool. He's the god of everything under the earth. Hazel can find caves, tunnels, trapdoors—"

"And it was our secret," Hazel grumbled.

Frank's face turned red. "Yeah, sorry. But if we can get close—"

"And if I can knock out the water cannons . . ." Percy nodded, like he was warming to the idea. "What do we do then?"

Frank checked his quiver.

"The rest is up to me," he said. "Let's go."

* * *

Hazel found them a tunnel with no problem. Passages that had been filled in years ago suddenly unfilled, changing direction to lead Hazel where she wanted to go. They crept along by the light of Percy's glowing sword, Riptide. Above, they heard the sounds of battle — kids shouting, Hannibal the elephant bellowing with glee, exploding noises, and water cannons firing. The tunnel shook. Dirt rained down on them.

"Ugh," Brooklyn muttered, brushing the dirt out of her hair. At least it wasn't getting to the top of her head, because she was wearing a helmet, but her dangling locks of hair . . . she'd just taken a bath too, come on!

"There's an opening just ahead," Hazel announced. "We'll come up ten feet from the east wall."

"How can you tell?" Percy asked.

"I don't know," she said. "But I'm sure."

"Could we tunnel straight under the wall?" Brooklyn wondered.

"No," Hazel said. "The engineers were smart. They built the walls on old foundations that go down to bedrock. And don't ask how I know. I just do."

Frank stumbled over something and cursed. Percy brought his sword around for more light. The thing Frank had tripped on was gleaming silver.

He crouched down.

"Don't touch it!" Hazel said.

Frank's hand stopped a few inches from the chunk of metal. It looked like a giant Hershey's Kiss, about the size of his fist.

"It's massive," he said. "Silver?"

"Platinum." Hazel sounded scared out of her wits. "It'll go away in a second. Please don't touch it. It's dangerous."

As they watched, the chunk of platinum sank into the ground.

Frank stared at Hazel. "How did you know?"

In the light of Percy's sword, Hazel looked as ghostly as a Lar. "I'll explain later," she promised.

Another explosion rocked the tunnel, and they forged ahead.

They popped out of a hole just where Hazel had predicted. In front of them, the fort's east wall loomed. Off to their left, Brooklyn could see part of the Fifth Cohort advancing, shields forming a shell over their heads and sides. They were trying to reach the main gates, but the defenders above pelted them with rocks and shot flaming bolts from the scorpions, blasting craters around their feet. A water cannon discharged with a jaw-rattling THRUM, and a jet of liquid carved a trench in the dirt right in front of the cohort.

Percy whistled. "That's a lot of pressure, all right."

The Third and Fourth Cohorts weren't even advancing. They stood back and laughed, watching their "allies" get beat up. The defenders clustered on the wall above the gates, yelling insults at the tortoise formation as it staggered back and forth.

"Let's shake things up." Frank reached in his quiver and pulled out an arrow. The iron tip was shaped like the nose cone of a rocket. An ultra thin gold rope trailed from the fletching.

"What does that do?" Percy asked. "Grappling hook?"

"It's called a hydra arrow," Frank said. "Can you knock out the water cannons?"

A defender appeared on the wall above them. "Hey!" he shouted to his buddies. "Check it out! More victims!"

"Perce," Brooklyn said, "now would be good."

More kids came across the battlements to laugh at them. A few ran to the nearest water cannon and swung the barrel toward her. Rude. Did they not know who she was?

Percy closed his eyes. He raised his hand.

Up on the wall, somebody yelled, "Open wide, losers!"

KA-BOOM!

The cannon exploded in a starburst of blue, green, and white. Defenders screamed as a watery shock wave flattened them against the battlements. Kids toppled over the walls but were snatched by giant eagles and carried to safety. Then the entire eastern wall shuddered as the explosion backed up through the pipelines. One after another, the water cannons on the battlements exploded. The scorpions' fires were doused. Defenders scattered in confusion or were tossed through the air, giving the rescue eagles quite a workout. At the main gates, the Fifth Cohort forgot about their formation. Mystified, they lowered their shields and stared at the chaos.

Frank shot his arrow. It streaked upward, carrying its glittering rope. When it reached the top, the metal point fractured into a dozen lines that lashed out and wrapped around anything they could find — parts of the wall, a scorpion, a broken water cannon, and a couple of defending campers, who yelped and found themselves slammed against the battlements as anchors. From the main rope, handholds extended at two-foot intervals, making a ladder.

"Go!" Frank said.

Percy grinned. "You first, Frank. This is your party."

Frank hesitated. Then he slung his bow on his back and began to climb. Brooklyn had started climbing when the defenders recovered their senses enough to sound the alarm.

Brooklyn glanced back at Fifth Cohort's main group. They were staring up at him, dumbfounded.

"Well?" Frank screamed. "Attack!"

Gwen was the first to unfreeze. She grinned and repeated the order. A cheer went up from the battlefield. Hannibal the elephant trumpeted with happiness, but Brooklyn continued to climb when she cursed under her breath at the feeling of someone cutting the rope.

Frank, who was already at the top, launched himself at the defenders, and they toppled like pins. He got to his feet and took command of the battlements, sweeping his pilum back and forth and knocking down defenders. Some shot arrows. Some tried to get under his guard with their swords, but Frank repelled them all. Then Hazel appeared next to him, swinging her big cavalry sword like she was born for battle.

Percy leaped onto the wall and raised Riptide.

"Fun," he said.

Brooklyn swung herself up, her paintball gun in her hands instead of her club. "Speak for yourself, I haven't hit anyone yet."

Together they cleared the defenders off the walls. Below them the gates broke. Hannibal barreled into the fort, arrows and rocks bouncing harmlessly off his Kevlar armor.

The Fifth Cohort charged in behind the elephant, and the battle went hand-to-hand.

Finally, from the edge of the Field of Mars, a battle cry went up. The Third and Fourth Cohorts ran to join the fight.

"A little late," Hazel grumbled.

"We can't let them get the banners," Frank said.

"No," Percy agreed. "Those are ours."

"My hands would be preferable," Brooklyn said. "But I wouldn't mind if we got it."

No more talk was necessary. They moved like a team, as if the four of them had been working together for years. They rushed down the interior steps and into the enemy base.