“I like to think of myself as captain,” Leo said. “Or supreme commander.”

“Brownies!” Aphros said proudly, shoving an old-fashioned picnic basket into Leo’s arms. It was surrounded by a bubble of air, which Leo hoped would keep the brownies from turning into saltwater fudge sludge. “In this basket you will also find the recipe. Not too much butter! That’s the trick. And I’ve given you a letter of introduction to Tiberinus, the god of the Tiber River. Once you reach Rome, your friend the daughter of Athena will need this.”

“Annabeth…” Leo said. “Okay, but why?”

Bythos laughed. “She follows the Mark of Athena, doesn’t she? Tiberinus can guide her in this quest. He’s an ancient, proud god who can be…difficult; but letters of introduction are everything to Roman spirits. This will convince Tiberinus to help her. Hopefully.”

“Hopefully,” Leo repeated.

Bythos produced three small pink pearls from his saddlebags. “And now, off with you, demigods! Good sailing!”

He threw a pearl at each of them in turn, and three shimmering pink bubbles of energy formed around them.

They began to rise through the water. Leo just had time to think: A hamster ball elevator? Then he gained speed and rocketed toward the distant glow of the sun above.

Chapter 25

Piper had a new entry in her top-ten list of Times Piper Felt Useless.

Fighting Shrimpzilla with a dagger and a pretty voice? Not so effective. Then the monster had sunk into the deep and disappeared along with three of her friends, and she’d been powerless to help them.

Afterward, Annabeth, Coach Hedge, and Buford the table rushed around repairing things so that the ship wouldn’t sink. Percy, despite being exhausted, searched the ocean for their missing friends. Jason, also exhausted, flew around the rigging like a blond Peter Pan, putting out fires from the second green explosion that had lit up the sky just above the mainmast.

As for Piper, all she could do was stare at her knife Katoptris, trying to locate Leo, Hazel, and Frank. The only images that came to her were ones she didn’t want to see: three black SUVs driving north from Charleston, packed with Roman demigods, Reyna sitting at the wheel of the lead car. Giant eagles escorted them from above. Every so often, glowing purple spirits in ghostly chariots appeared out of the countryside and fell in behind them, thundering up I-95 toward New York and Camp Half-Blood.

Piper concentrated harder. She saw the nightmarish images she had seen before: the human-headed bull rising from the water, then the dark well-shaped room filling with black water as Jason, Percy, and she struggled to stay afloat.

She sheathed Katoptris, wondering how Helen of Troy had stayed sane during the Trojan War, if this blade had been her only source of news. Then she remembered that everyone around Helen had been slaughtered by the invading Greek army. Maybe she hadn’t stayed sane.

By the time the sun rose, none of them had slept. Percy had scoured the seafloor and found nothing. The Argo II was no longer in danger of sinking, though without Leo, they couldn’t do full repairs. The ship was capable of sailing, but no one suggested leaving the area—not without their missing friends.

Piper and Annabeth sent a dream vision to Camp Half-Blood, warning Chiron of what had happened with the Romans at Fort Sumter. Annabeth explained her exchange of words with Reyna. Piper relayed the vision from her knife about the SUVs racing north. The kindly centaur’s face seemed to age thirty years during the course of their conversation, but he assured them he would see to the defenses of the camp. Tyson, Mrs. O’Leary, and Ella had arrived safely. If necessary, Tyson could summon an army of Cyclopes to the camp’s defense, and Ella and Rachel Dare were already comparing prophecies, trying to learn more about what the future held. The job of the seven demigods aboard the Argo II, Chiron reminded them, was to finish the quest and come back safely.

After the Iris-message, the demigods paced the deck in silence, staring at the water and hoping for a miracle.

When it finally came—three giant pink bubbles bursting at the surface off the starboard bow and ejecting Frank, Hazel, and Leo—Piper went a little crazy. She cried out with relief and dove straight into the water.

What was she thinking? She didn’t take a rope or a life vest or anything. But at the moment, she was just so happy that she paddled over to Leo and kissed him on the cheek, which kind of surprised him.

“Miss me?” Leo laughed.

Piper was suddenly furious. “Where were you? How are you guys alive?”

“Long story,” he said. A picnic basket bobbed to the surface next to him. “Want a brownie?”

Once they got on board and changed into dry clothes (poor Frank had to borrow a pair of too-small pants from Jason) the crew all gathered on the quarterdeck for a celebratory breakfast—except for Coach Hedge, who grumbled that the atmosphere was getting too cuddly for his tastes and went below to hammer out some dents in the hull. While Leo fussed over his helm controls, Hazel and Frank related the story of the fish-centaurs and their training camp.

“Incredible,” Jason said. “These are really good brownies.”

“That’s your only comment?” Piper demanded.

He looked surprised. “What? I heard the story. Fish-centaurs. Merpeople. Letter of intro to the Tiber River god. Got it. But these brownies—”

“I know,” Frank said, his mouth full. “Try them with Esther’s peach preserves.”

“That,” Hazel said, “is incredibly disgusting.”

“Pass me the jar, man,” Jason said.

Hazel and Piper exchanged a look of total exasperation. Boys.

Percy, for his part, wanted to hear every detail about the aquatic camp. He kept coming back to one point: “They didn’t want to meet me?”

“It wasn’t that,” Hazel said. “Just…undersea politics, I guess. The merpeople are territorial. The good news is they’re taking care of that aquarium in Atlanta. And they’ll help protect the Argo II as we cross the Atlantic.”

Percy nodded absently. “But they didn’t want to meet me?”

Annabeth swatted his arm. “Come on, Seaweed Brain! We’ve got other things to worry about.”

“She’s right,” Hazel said. “After today, Nico has less than two days. The fish-centaurs said we have to rescue him. He’s essential to the quest somehow.”

She looked around defensively, as if waiting for someone to argue. No one did. Piper tried to imagine what Nico di Angelo was feeling, stuck in a jar with only two pomegranate seeds left to sustain him, and no idea whether he would be rescued. It made Piper anxious to reach Rome, even though she had a horrible feeling she was sailing toward her own sort of prison—a dark room filled with water.

“Nico must have information about the Doors of Death,” Piper said. “We’ll save him, Hazel. We can make it in time. Right, Leo?”

“What?” Leo tore his eyes away from the controls. “Oh, yeah. We should reach the Mediterranean tomorrow morning. Then spend the rest of that day sailing to Rome, or flying, if I can get the stabilizer fixed by then.…”

Jason suddenly looked as though his brownie with peach preserves didn’t taste so good. “Which will put us in Rome on the last possible day for Nico. Twenty-four hours to find him—at most.”

Percy crossed his legs. “And that’s only part of the problem. There’s the Mark of Athena, too.”

Annabeth didn’t seem happy with the change of topic. She rested her hand on her backpack, which, since they’d left Charleston, she always seemed to have with her.

She opened the bag and brought out a thin bronze disk the diameter of a donut. “This is the map that I found at Fort Sumter. It’s…”

She stopped abruptly, staring at the smooth bronze surface. “It’s blank!”

Percy took it and examined both sides. “It wasn’t like this earlier?”

“No! I was looking at it in my cabin and…” Annabeth muttered under her breath. “It must be like the Mark of Athena. I can only see it when I’m alone. It won’t show itself to other demigods.”

Frank scooted back like the disk might explode. He had an orange-juice mustache and a brownie-crumb beard that made Piper want to hand him a napkin.

“What did it have on it?” Frank asked nervously. “And what is the Mark of Athena? I still don’t get it.”

Annabeth took the disk from Percy. She turned it in the sunlight, but it remained blank. “The map was hard to read, but it showed a spot on the Tiber River in Rome. I think that’s where my quest starts…the path I’ve got to take to follow the Mark.”

“Maybe that’s where you meet the river god Tiberinus,” Piper said. “But what is the Mark?”

“The coin,” Annabeth murmured.

Percy frowned. “What coin?”

Annabeth dug into her pocket and brought out a silver drachma. “I’ve been carrying this ever since I saw my mom at Grand Central. It’s an Athenian coin.”

She passed it around. While each demigod looked at it, Piper had a ridiculous memory of show-and-tell in elementary school.

“An owl,” Leo noted. “Well, that makes sense. I guess the branch is an olive branch? But what’s this inscription, ΑΘΕ—Area Of Effect?”

“It’s alpha, theta, epsilon,” Annabeth said. “In Greek it stands for Of The Athenians…or you could read it as the children of Athena. It’s sort of the Athenian motto.”

“Like SPQR for the Romans,” Piper guessed.

Annabeth nodded. “Anyway, the Mark of Athena is an owl, just like that one. It appears in fiery red. I’ve seen it in my dreams. Then twice at Fort Sumter.”

She described what had happened at the fort—the voice of Gaea, the spiders in the garrison, the Mark burning them away. Piper could tell it wasn’t easy for her to talk about.

Percy took Annabeth’s hand. “I should have been there for you.”

“But that’s the point,” Annabeth said. “No one can be there for me. When I get to Rome, I’ll have to strike out on my own. Otherwise, the Mark won’t appear. I’ll have to follow it to…to the source.”

Frank took the coin from Leo. He stared at the owl. “The giants’ bane stands gold and pale, Won with pain from a woven jail.” He looked up at Annabeth. “What is it…this thing at the source?”

Before Annabeth could answer, Jason spoke up.

“A statue,” he said. “A statue of Athena. At least…that’s my guess.”

Piper frowned. “You said you didn’t know.”

“I don’t. But the more I think about it…there’s only one artifact that could fit the legend.” He turned to Annabeth. “I’m sorry. I should have told you everything I’ve heard, much earlier. But honestly, I was scared. If this legend is true—”

“I know,” Annabeth said. “I figured it out, Jason. I don’t blame you. But if we manage to save the statue, Greek and Romans together…Don’t you see? It could heal the rift.”