She thought the plot was silly—a princess escapes her minders and falls in love with an American journalist in Rome—but she suspected her dad liked it because it reminded him of his own romance with the goddess Athena: another impossible pairing that couldn’t end happily. Her dad was nothing like Gregory Peck. Athena certainly wasn’t anything like Audrey Hepburn. But Annabeth knew that people saw what they wanted to see. They didn’t need the Mist to warp their perceptions.

As the baby-blue scooter zipped through the streets of Rome, the goddess Rhea Silvia gave Annabeth a running commentary on how the city had changed over the centuries.

“The Sublician Bridge was over there,” she said, pointing to a bend in the Tiber. “You know, where Horatius and his two friends defended the city from an invading army? Now, there was a brave Roman!”

“And look, dear,” Tiberinus added, “that’s the place where Romulus and Remus washed ashore.”

He seemed to be talking about a spot on the riverside where some ducks were making a nest out of torn-up plastic bags and candy wrappers.

“Ah, yes,” Rhea Silvia sighed happily. “You were so kind to flood yourself and wash my babies ashore for the wolves to find.”

“It was nothing,” Tiberinus said.

Annabeth felt light-headed. The river god was talking about something that had happened thousands of years ago, when this area was nothing but marshes and maybe some shacks. Tiberinus saved two babies, one of whom went on to found the world’s greatest empire. It was nothing.

Rhea Silvia pointed out a large modern apartment building. “That used to be a temple to Venus. Then it was a church. Then a palace. Then an apartment building. It burned down three times. Now it’s an apartment building again. And that spot right there—”

“Please,” Annabeth said. “You’re making me dizzy.”

Rhea Silvia laughed. “I’m sorry, dear. Layers upon layers of history here, but it’s nothing compared to Greece. Athens was old when Rome was a collection of mud huts. You’ll see, if you survive.”

“Not helping,” Annabeth muttered.

“Here we are,” Tiberinus announced. He pulled over in front of a large marble building, the facade covered in city grime but still beautiful. Ornate carvings of Roman gods decorated the roofline. The massive entrance was barred with iron gates, heavily padlocked.

“I’m going in there?” Annabeth wished she’d brought Leo, or at least borrowed some wire cutters from his tool belt.

Rhea Silvia covered her mouth and giggled. “No, my dear. Not in it. Under it.”

Tiberinus pointed to a set of stone steps on the side of the building—the sort that would have led to a basement apartment if this place were in Manhattan.

“Rome is chaotic aboveground,” Tiberinus said, “but that’s nothing compared to below ground. You must descend into the buried city, Annabeth Chase. Find the altar of the foreign god. The failures of your predecessors will guide you. After that…I do not know.”

Annabeth’s backpack felt heavy on her shoulders. She’d been studying the bronze map for days now, scouring Daedalus’s laptop for information. Unfortunately, the few things she had learned made this quest seem even more impossible. “My siblings…none of them made it all the way to the shrine, did they.”

Tiberinus shook his head. “But you know what prize awaits, if you can liberate it.”

“Yes,” Annabeth said.

“It could bring peace to the children of Greece and Rome,” Rhea Silvia said. “It could change the course of the coming war.”

“If I live,” Annabeth said.

Tiberinus nodded sadly. “Because you also understand the guardian you must face?”

Annabeth remembered the spiders at Fort Sumter, and the dream Percy had described—the hissing voice in the dark. “Yes.”

Rhea Silvia looked at her husband. “She is brave. Perhaps she is stronger than the others.”

“I hope so,” said the river god. “Good-bye, Annabeth Chase. And good luck.”

Rhea Silvia beamed. “We have such a lovely afternoon planned! Off to shop!”

Gregory Peck and Audrey Hepburn sped off on their baby-blue motorbike. Then Annabeth turned and descended the steps alone.

She’d been underground plenty of times.

But halfway down the steps, she realized just how long it had been since she’d adventured by herself. She froze.

Gods…she hadn’t done something like this since she was a kid. After running away from home, she’d spent a few weeks surviving on her own, living in alleyways and hiding from monsters until Thalia and Luke took her under their wings. Then, once she’d arrived at Camp Half-Blood, she’d lived there until she was twelve. After that, all her quests had been with Percy or her other friends.

The last time she had felt this scared and alone, she’d been seven years old. She remembered the day Thalia, Luke, and she had wandered into a Cyclopes’ lair in Brooklyn. Thalia and Luke had gotten captured, and Annabeth had had to cut them free. She still remembered shivering in a dark corner of that dilapidated mansion, listening to the Cyclopes mimicking her friends’ voices, trying to trick her into coming out into the open.

What if this is a trick, too? she wondered. What if those other children of Athena died because Tiberinus and Rhea Silvia led them into a trap? Would Gregory Peck and Audrey Hepburn do something like that?

She forced herself to keep going. She had no choice. If the Athena Parthenos was really down here, it could decide the fate of the war. More importantly, it could help her mom. Athena needed her.

At the bottom of the steps she reached an old wooden door with an iron pull ring. Above the ring was a metal plate with a keyhole. Annabeth started considering ways to pick the lock, but as soon as she touched the pull ring, a fiery shape burned in the middle of the door: the silhouette of Athena’s owl. Smoke plumed from the keyhole. The door swung inward.

Annabeth looked up one last time. At the top of the stairwell, the sky was a square of brilliant blue. Mortals would be enjoying the warm afternoon. Couples would be holding hands at the cafés. Tourists would be bustling through the shops and museums. Regular Romans would be going about their daily business, probably not considering the thousands of years of history under their feet, and definitely unaware of the spirits, gods, and monsters that still dwelt here, or the fact that their city might be destroyed today unless a certain group of demigods succeeded in stopping the giants.

Annabeth stepped through the doorway.

She found herself in a basement that was an architectural cyborg. Ancient brick walls were crisscrossed with modern electrical cables and plumbing. The ceiling was held up with a combination of steel scaffolding and old granite Roman columns.

The front half of the basement was stacked with crates. Out of curiosity, Annabeth opened a few. Some were packed with multicolored spools of string—like for kites or arts and crafts projects. Other crates were full of cheap plastic gladiator swords. Maybe at one point this had been a storage area for a tourist shop.

In the back of the basement, the floor had been excavated, revealing another set of steps—these of white stone—leading still deeper underground.

Annabeth crept to the edge. Even with the glow cast by her dagger, it was too dark to see below. She rested her hand on the wall and found a light switch.

She flipped it. Glaring white fluorescent bulbs illuminated the stairs. Below, she saw a mosaic floor decorated with deer and fauns—maybe a room from an Ancient Roman villa, just stashed away under this modern basement along with the crates of string and plastic swords.

She climbed down. The room was about twenty feet square. The walls had once been brightly painted, but most of the frescoes had peeled or faded. The only exit was a hole dug in one corner of the floor where the mosaic had been pulled up. Annabeth crouched next to the opening. It dropped straight down into a larger cavern, but Annabeth couldn’t see the bottom.

She heard running water maybe thirty or forty feet below. The air didn’t smell like a sewer—just old and musty, and slightly sweet, like moldering flowers. Perhaps it was an old water line from the aqueducts. There was no way down.

“I’m not jumping,” she muttered to herself.

As if in reply, something glowed in the darkness. The Mark of Athena blazed to life at the bottom of the cavern, revealing glistening brickwork along a subterranean canal forty feet below. The fiery owl seemed to be taunting her: Well, this is the way, kid. So you’d better figure something out.

Annabeth considered her options. Too dangerous to jump. No ladders or ropes. She thought about borrowing some metal scaffolding from above to use as a fire pole, but it was all bolted in place. Besides, she didn’t want to cause the building to collapse on top of her.

Frustration crawled through her like an army of termites. She had spent her life watching other demigods gain amazing powers. Percy could control water. If he were here, he could raise the water level and simply float down. Hazel, from what she had said, could find her way underground with flawless accuracy and even create or change the course of tunnels. She could easily make a new path. Leo would pull just the right tools from his belt and build something to do the job. Frank could turn into a bird. Jason could simply control the wind and float down. Even Piper with her charmspeak…she could have convinced Tiberinus and Rhea Silvia to be a little more helpful.

What did Annabeth have? A bronze dagger that did nothing special, and a cursed silver coin. She had her backpack with Daedalus’s laptop, a water bottle, a few pieces of ambrosia for emergencies, and a box of matches—probably useless, but her dad had drilled into her head that she should always have a way to make fire.

She had no amazing powers. Even her one true magic item, her New York Yankees cap of invisibility, had stopped working, and was still back in her cabin on the Argo II.

You’ve got your intelligence, a voice said. Annabeth wondered if Athena was speaking to her, but that was probably just wishful thinking.

Intelligence…like Athena’s favorite hero, Odysseus. He’d won the Trojan War with cleverness, not strength. He had overcome all sorts of monsters and hardships with his quick wits. That’s what Athena valued.

Wisdom’s daughter walks alone.

That didn’t mean just without other people, Annabeth realized. It meant without any special powers.

Okay…so how to get down there safely and make sure she had a way to get out again if necessary?

She climbed back to the basement and stared at the open crates. Kite string and plastic swords. The idea that came to her was so ridiculous, she almost had to laugh; but it was better than nothing.

She set to work. Her hands seemed to know exactly what to do. Sometimes that happened, like when she was helping Leo with the ship’s machinery or drawing architectural plans on the computer. She’d never made anything out of kite string and plastic swords, but it seemed easy, natural. Within minutes she’d used a dozen balls of string and a crateful of swords to create a makeshift rope ladder—a braided line, woven for strength yet not too thick, with swords tied at two-foot intervals to serve as hand- and footholds.