She sat on her bunk, using one of Daedalus’s 3-D-rendering programs to study a model of the Parthenon in Athens. She’d always yearned to visit it, both because she loved architecture and because it was the most famous temple to her mother.

Now she might get her wish, if they lived long enough to reach Greece. But the more she thought about the Mark of Athena, and the old Roman legend Reyna had mentioned, the more nervous she got.

She didn’t want to, but she recalled her argument with her mother. Even after so many weeks, the words still stung.

Annabeth had been riding the subway back from the Upper East Side after visiting Percy’s mom. During those long months when Percy was missing, Annabeth made the trip at least once a week—partly to give Sally Jackson and her husband Paul an update on the search, and partly because Annabeth and Sally needed to lift each other’s spirits and convince one another that Percy would be fine.

The spring had been especially hard. By then, Annabeth had reason to hope Percy was alive, since Hera’s plan seemed to involve sending him to the Roman side, but she couldn’t be sure where he was. Jason had remembered his old camp’s location more or less, but all the Greeks’ magic—even that of the campers of Hecate’s cabin—couldn’t confirm that Percy was there, or anywhere. He seemed to have disappeared from the planet. Rachel the Oracle had tried to read the future, and while she couldn’t see much, she’d been certain that Leo needed to finish the Argo II before they could contact the Romans.

Nevertheless, Annabeth had spent every spare moment scouring all sources for any rumors of Percy. She had talked to nature spirits, read legends about Rome, dug for clues on Daedalus’s notebook, and spent hundreds of golden drachmas on Iris-messages to every friendly spirit, demigod, or monster she’d ever met, all with no luck.

That particular afternoon, coming back from Sally’s, Annabeth had felt even more drained than usual. She and Sally had first cried and then attempted to pull themselves together, but their nerves were frayed. Finally Annabeth took the Lexington Avenue subway down to Grand Central.

There were other ways to get back to her high school dorm from the Upper East Side, but Annabeth liked going through Grand Central Terminal. The beautiful design and the vast open space reminded her of Mount Olympus. Grand buildings made her feel better—maybe because being in a place so permanent made her feel more permanent.

She had just passed Sweet on America, the candy shop where Percy’s mom used to work, and was thinking about going inside to buy some blue candy for old times’ sake, when she saw Athena studying the subway map on the wall.

“Mother!” Annabeth couldn’t believe it. She hadn’t seen her mom in months—not since Zeus had closed the gates of Olympus and forbidden all communication with demigods.

Many times, Annabeth had tried to call on her mom anyway, pleading for guidance, sending up burnt offerings with every meal at camp. She’d had no response. Now here was Athena, dressed in jeans and hiking boots and a red flannel shirt, her dark hair cascading over her shoulders. She held a backpack and a walking stick like she was prepared for a long journey.

“I must return home,” Athena murmured, studying the map. “The way is complex. I wish Odysseus were here. He would understand.”

“Mom!” Annabeth said. “Athena!”

The goddess turned. She seemed to look right through Annabeth with no recognition.

“That was my name,” the goddess said dreamily. “Before they sacked my city, took my identity, made me this.” She looked at her clothes in disgust. “I must return home.”

Annabeth stepped back in shock. “You’re…you’re Minerva?”

“Don’t call me that!” The goddess’s gray eyes flared with anger. “I used to carry a spear and a shield. I held victory in the palm of my hand. I was so much more than this.”

“Mom.” Annabeth’s voice trembled. “It’s me, Annabeth. Your daughter.”

“My daughter…” Athena repeated. “Yes, my children will avenge me. They must destroy the Romans. Horrible, dishonorable, copycat Romans. Hera argued that we must keep the two camps apart. I said, No, let them fight. Let my children destroy the usurpers.”

Annabeth’s heartbeat thumped in her ears. “You wanted that? But you’re wise. You understand warfare better than any—”

“Once!” the goddess said. “Replaced. Sacked. Looted like a trophy and carted off—away from my beloved homeland. I lost so much. I swore I would never forgive. Neither would my children.” She focused more closely on Annabeth. “You are my daughter?”

“Yes.”

The goddess fished something from the pocket of her shirt—an old-fashioned subway token—and pressed it into Annabeth’s hand.

“Follow the Mark of Athena,” the goddess said. “Avenge me.”

Annabeth had looked at the coin. As she watched, it changed from a New York subway token to an ancient silver drachma, the kind used by Athenians. It showed an owl, Athena’s sacred animal, with an olive branch on one side and a Greek inscription on the other.

The Mark of Athena.

At the time, Annabeth had had no idea what it meant. She didn’t understand why her mom was acting like this. Minerva or not, she shouldn’t be so confused.

“Mom…” She tried to make her tone as reasonable as possible. “Percy is missing. I need your help.” She had started to explain Hera’s plan for bringing the camps together to battle Gaea and the giants, but the goddess stamped her walking stick against the marble floor.

“Never!” she said. “Anyone who helps Rome must perish. If you would join them, you are no child of mine. You have already failed me.”

“Mother!”

“I care nothing about this Percy. If he has gone over to the Romans, let him perish. Kill him. Kill all the Romans. Find the Mark, follow it to its source. Witness how Rome has disgraced me, and pledge your vengeance.”

“Athena isn’t the goddess of revenge.” Annabeth’s nails bit into her palms. The silver coin seemed to grow warmer in her hand. “Percy is everything to me.”

“And revenge is everything to me,” the goddess snarled. “Which of us is wiser?”

“Something is wrong with you. What’s happened?”

“Rome happened!” the goddess said bitterly. “See what they have done, making a Roman of me. They wish me to be their goddess? Then let them taste their own evil. Kill them, child.”

“No!”

“Then you are nothing.” The goddess turned to the subway map. Her expression softened, becoming confused and unfocused. “If I could find the route…the way home, then perhaps— But, no. Avenge me or leave me. You are no child of mine.”

Annabeth’s eyes stung. She thought of a thousand horrible things she wanted to say, but she couldn’t. She had turned and fled.

She’d tried to throw away the silver coin, but it simply reappeared in her pocket, the way Riptide did for Percy. Unfortunately, Annabeth’s drachma had no magical powers—at least nothing useful. It only gave her nightmares, and no matter what she tried, she couldn’t get rid of it.

Now, sitting in her cabin aboard the Argo II, she could feel the coin growing warm in her pocket. She stared at the model of the Parthenon on her computer screen and thought about the argument with Athena. Phrases she’d heard over the last few days swirled in her head: A talented friend, ready for her visitor. No one will retrieve that statue. Wisdom’s daughter walks alone.

She was afraid she finally understood what it all meant. She prayed to the gods that she was wrong.

A knock on her door made her jump.

She hoped it might be Percy, but instead Frank Zhang poked his head in.

“Um, sorry,” he said. “Could I—?”

She was so startled to see him, it took her a moment to realize he wanted to come in.

“Sure,” she said. “Yes.”

He stepped inside, looking around the cabin. There wasn’t much to see. On her desk sat a stack of books, a journal and pen, and a picture of her dad flying his Sopwith Camel biplane, grinning and giving the thumbs-up. Annabeth liked that photo. It reminded her of the time she’d felt closest to him, when he’d strafed an army of monsters with Celestial bronze machine guns just to protect her—pretty much the best present a girl could hope for.

Hanging from a hook on the wall was her New York Yankees cap, her most prized possession from her mom. Once, the cap had had the power to turn its wearer invisible. Since Annabeth’s argument with Athena, the cap had lost its magic. Annabeth wasn’t sure why, but she’d stubbornly brought it along on the quest. Every morning she would try it on, hoping it would work again. So far it had only served as a reminder of her mother’s wrath.

Otherwise, her cabin was bare. She kept it clean and simple, which helped her to think. Percy didn’t believe it because she always made excellent grades, but like most demigods, she was ADHD. When there were too many distractions in her personal space, she was never able to focus.

“So…Frank,” she ventured. “What can I do for you?”

Out of all the kids on the ship, Frank was the one she thought least likely to pay her a visit. She didn’t feel any less confused when he blushed and pulled his Chinese handcuffs out of his pocket.

“I don’t like being in the dark about this,” he muttered. “Could you show me the trick? I didn’t feel comfortable asking anyone else.”

Annabeth processed his words with a slight delay. Wait…Frank was asking her for help? Then it dawned on her: of course, Frank was embarrassed. Leo had been razzing him pretty hard. Nobody liked being a laughingstock. Frank’s determined expression said he never wanted that to happen again. He wanted to understand the puzzle, without the iguana solution.

Annabeth felt strangely honored. Frank trusted her not to make fun of him. Besides, she had a soft spot for anyone who was seeking knowledge—even about something as simple as Chinese handcuffs.

She patted the bunk next to her. “Absolutely. Sit down.”

Frank sat on the edge of the mattress, as if preparing for a quick escape. Annabeth took the Chinese handcuffs and held them next to her computer.

She hit the key for an infrared scan. A few seconds later a 3-D model of the Chinese handcuffs appeared on the screen. She turned the laptop so that Frank could see.

“How did you do that?” he marveled.

“Cutting-edge Ancient Greek technology,” she said. “Okay, look. The structure is a cylindrical biaxial braid, so it has excellent resilience.” She manipulated the image so it squeezed in and out like an accordion. “When you put your fingers inside, it loosens. But when you try to remove them, the circumference shrinks as the braid catches and tightens. There’s no way you can pull free by struggling.”

Frank stared at her blankly. “But what’s the answer?”

“Well…” She showed him some of her calculations—how the handcuffs could resist tearing under incredible stress, depending on the material used in the braid. “Pretty amazing for a woven structure, right? Doctors use it for traction, and electrical contractors—”