Piper shuddered. She didn’t know what time it was, but the sun was already starting to sink. How had the day passed so quickly? She would have welcomed sundown for the cooler temperatures, except it was also their deadline. A cool night breeze wouldn’t mean much if they were dead. Besides, tomorrow was July 1, the Kalends of July. If their information was correct, it would be Nico di Angelo’s last day of life, and the day Rome was destroyed.

“Stop,” Jason said.

Piper wasn’t sure what was wrong. Then she realized she could hear running water up ahead. They crept through the trees and found themselves on the bank of a river. It was maybe forty feet wide but only a few inches deep, a silver sheet of water racing over a smooth bed of stones. A few yards downstream, the rapids plunged into a dark blue swimming hole.

Something about the river bothered her. The cicadas in the trees had gone quiet. No birds were chirping. It was as if the water was giving a lecture and would only allow its own voice.

But the more Piper listened, the more inviting the river seemed. She wanted to take a drink. Maybe she should take off her shoes. Her feet could really use a soak. And that swimming hole…it would be so nice to jump in with Jason and relax in the shade of the trees, floating in the nice cool water. So romantic.

Piper shook herself. These thoughts weren’t hers. Something was wrong. It almost felt like the river was charmspeaking.

Jason sat on a rock and started taking off his shoes. He grinned at the swimming hole like he couldn’t wait to get in.

“Cut it out!” Piper yelled at the river.

Jason looked startled. “Cut what out?”

“Not you,” Piper said. “Him.”

She felt silly pointing at the water, but she was certain it was working some sort of magic, swaying their feelings.

Just when she thought she had lost it and Jason would tell her so, the river spoke: Forgive me. Singing is one of the few pleasures I have left.

A figure emerged from the swimming hole as if rising on an elevator.

Piper’s shoulders tensed. It was the creature she’d seen in her knife blade, the bull with the human face. His skin was as blue as the water. His hooves levitated on the river’s surface. At the top of his bovine neck was the head of a man with short curly black hair, a beard done in ringlets Ancient Greek style, deep, mournful eyes behind bifocal glasses, and a mouth that seemed set in a permanent pout. Sprouting from the left side of his head was a single bull’s horn—a curved black-and-white one like warriors might turn into drinking cups. The imbalance made his head tilt to the left, so that he looked like he was trying to get water out of his ear.

“Hello,” he said sadly. “Come to kill me, I suppose.”

Jason put his shoes back on and stood slowly. “Um, well—”

“No!” Piper intervened. “I’m sorry. This is embarrassing. We didn’t want to bother you, but Hercules sent us.”

“Hercules!” The bull-man sighed. His hooves pawed the water as if ready to charge. “To me, he’ll always be Heracles. That’s his Greek name, you know: the glory of Hera.”

“Funny name,” Jason said. “Since he hates her.”

“Indeed,” the bull-man said. “Perhaps that’s why he didn’t protest when the Romans renamed him Hercules. Of course, that’s the name most people know him by…his brand, if you will. Hercules is nothing if not image-conscious.”

The bull-man spoke with bitterness but familiarity, as if Hercules was an old friend who had lost his way.

“You’re Achelous?” Piper asked.

The bull-man bent his front legs and lowered his head in a bow, which Piper found both sweet and a little sad. “At your service. River god extraordinaire. Once the spirit of the mightiest river in Greece. Now sentenced to dwell here, on the opposite side of the island from my old enemy. Oh, the gods are cruel! But whether they put us so close together to punish me or Hercules, I have never been sure.”

Piper wasn’t sure what he meant, but the background noise of the river was invading her mind again—reminding her how hot and thirsty she felt, how pleasant a nice swim would be. She tried to focus.

“I’m Piper,” she said. “This is Jason. We don’t want to fight. It’s just that Heracles—Hercules—whoever he is, got mad at us and sent us here.”

She explained about their quest to the ancient lands to stop the giants from waking Gaea. She described how their team of Greeks and Romans had come together, and how Hercules had thrown a temper tantrum when he found out Hera was behind it.

Achelous kept tipping his head to the left, so Piper wasn’t sure if he was dozing off or dealing with one-horn fatigue.

When she was done, Achelous regarded her as if she were developing a regrettable skin rash. “Ah, my dear…the legends are true, you know. The spirits, the water cannibals.”

Piper had to fight back a whimper. She hadn’t told Achelous anything about that. “H-how—?”

“River gods know many things,” he said. “Alas, you are focusing on the wrong story. If you had made it to Rome, the story of the flood would have served you better.”

“Piper?” Jason asked. “What’s he talking about?”

Her thoughts were suddenly as jumbled as kaleidoscope glass. The story of the flood…If you had made it to Rome.

“I—I’m not sure,” she said, though the mention of a flood story rang a distant bell. “Achelous, I don’t understand—”

“No, you don’t,” the river god sympathized. “Poor thing. Another girl stuck with a son of Zeus.”

“Wait a minute,” Jason said. “It’s Jupiter, actually. And how does that make her a poor thing?”

Achelous ignored him. “My girl, do you know the cause of my fight with Hercules?”

“It was over a woman,” Piper recalled. “Deianira?”

“Yes.” Achelous heaved a sigh. “And do you know what happened to her?”

“Uh…” Piper glanced at Jason.

He took out his guidebook and began flipping through pages. “It doesn’t really—”

Achelous snorted indignantly. “What is that?”

Jason blinked. “Just…The Hercules Guide to Mare Nostrum. He gave us the guidebook so—”

“That is not a book,” Achelous insisted. “He gave you that just to get under my skin, didn’t he? He knows I hate those things.”

“You hate…books?” Piper asked.

“Bah!” Achelous’s face flushed, turning his blue skin eggplant purple. “That’s not a book.”

He pawed the water. A scroll shot from the river like a miniature rocket and landed in front of him. He nudged it open with his hooves. The weathered yellow parchment unfurled, covered with faded Latin script and elaborate hand-drawn pictures.

“This is a book!” Achelous said. “Oh, the smell of sheepskin! The elegant feel of the scroll unrolling beneath my hooves. You simply can’t duplicate it in something like that.”

He nodded indignantly at the guidebook in Jason’s hand. “You young folks today and your newfangled gadgets. Bound pages. Little compact squares of text that are not hoof-friendly. That’s a bound book, a b-book, if you must. But it’s not a traditional book. It’ll never replace the good old-fashioned scroll!”

“Um, I’ll just put this away now.” Jason slipped the guidebook in his back pocket the way he might holster a dangerous weapon.

Achelous seemed to calm down a little, which was a relief to Piper. She didn’t need to get run over by a one-horned bull with a scroll obsession.

“Now,” Achelous said, tapping a picture on his scroll. “This is Deianira.”

Piper knelt down to look. The hand-painted portrait was small, but she could tell the woman had been very beautiful, with long dark hair, dark eyes, and a playful smile that probably drove guys crazy.

“Princess of Calydon,” the river god said mournfully. “She was promised to me, until Hercules butted in. He insisted on combat.”

“And he broke off your horn?” Jason guessed.

“Yes,” Achelous said. “I could never forgive him for that. Horribly uncomfortable, having only one horn. But the situation was worse for poor Deianira. She could have had a long, happy life married to me.”

“A man-headed bull,” Piper said, “who lives in a river.”

“Exactly,” Achelous agreed. “It seems impossible she would refuse, eh? Instead, she went off with Hercules. She picked the handsome, flashy hero over the good, faithful husband who would have treated her well. What happened next? Well, she should have known. Hercules was much too wrapped up in his own problems to be a good husband. He had already murdered one wife, you know. Hera cursed him, so he flew into a rage and killed his entire family. Horrible business. That’s why he had to do those twelve labors as penance.”

Piper felt appalled. “Wait…Hera made him crazy, and Hercules had to do the penance?”

Achelous shrugged. “The Olympians never seem to pay for their crimes. And Hera has always hated the sons of Zeus…or Jupiter.” He glanced distrustfully at Jason. “At any rate, my poor Deianira had a tragic end. She became jealous of Hercules’s many affairs. He gallivanted all over the world, you see, just like his father Zeus, flirting with every woman he met. Finally Deianira got so desperate she listened to bad advice. A crafty centaur named Nessus told her that if she wanted Hercules to be faithful forever, she should spread some centaur blood on the inside of Hercules’s favorite shirt. Unfortunately Nessus was lying because he wanted revenge on Hercules. Deianira followed his instructions, but instead of making Hercules a faithful husband—”

“Centaur blood is like acid,” Jason said.

“Yes,” Achelous said. “Hercules died a painful death. When Deianira realized what she’d done, she…” The river god drew a line across his neck.

“That’s awful,” Piper said.

“And the moral, my dear?” Achelous said. “Beware the sons of Zeus.”

Piper couldn’t look at her boyfriend. She wasn’t sure she could mask the uneasiness in her eyes. Jason would never be like Hercules. But the story played into all her fears. Hera had manipulated their relationship, just as she had manipulated Hercules. Piper wanted to believe that Jason could never go into a murderous frenzy like Hercules had. Then again, only four days ago he had been controlled by an eidolon and almost killed Percy Jackson.

“Hercules is a god now,” Achelous said. “He married Hebe, the youth goddess, but still he is rarely at home. He dwells here on this island, guarding those silly pillars. He says Zeus makes him do this, but I think he prefers being here to Mount Olympus, nursing his bitterness and mourning his mortal life. My presence reminds him of his failures—especially the woman who finally killed him. And his presence reminds me of poor Deianira, who could have been my wife.”

The bull-man tapped the scroll, which rolled itself up and sank into the water.