“Yay!” Tyson cried as we came through the doorway. “Come in! We are having our great opening today!”

“Grand opening,” Ella corrected, fussing over a platter of cupcakes and a bunch of balloons at the information desk. “Welcome to Cyclops Books and Prophecies and Also an Orange Cat.”

“That wouldn’t all fit on the sign,” Tyson confided.

“It should have fit on the sign,” Ella said. “We need a bigger sign.”

On top of the old-fashioned cash register, Aristophanes yawned as if it was all the same to him. He was wearing a tiny party hat and an expression that said, I am only wearing this because demigods don’t have phone cameras or Instagram.

“Customers can get prophecies for their quests!” Tyson explained, pointing at his chest, which was covered even more densely with Sibylline verse. “They can pick up the latest books, too!”

“I recommend the 1924 Farmer’s Almanac,” Ella told us. “Would you like a copy?”

“Ah…maybe next time,” I said. “We were told you had a prophecy for us?”

“Yep, yep.” Ella ran her finger down Tyson’s ribs, scanning for the correct lines.

The Cyclops squirmed and giggled.

“Here,” Ella said. “Over his spleen.”

Wonderful, I thought. The Prophecy of Tyson’s Spleen.

Ella read aloud:

“O son of Zeus the final challenge face

The tow’r of Nero two alone ascend

Dislodge the beast that hast usurped thy place.”

I waited.

Ella nodded. “Yep, yep, yep. That’s it.” She went back to her cupcakes and balloons.

“That can’t be it,” I complained. “That makes no poetic sense. It’s not a haiku. It’s not a sonnet. It’s not…Oh.”

Meg squinted at me. “Oh, what?”

“Oh, as in Oh, no.” I remembered a dour young man I’d met in medieval Florence. It had been a long time ago, but I never forgot someone who invented a new type of poetry. “It’s terza rima.”

“Who?” Meg asked.

“It’s a style Dante invented. In The Inferno. Three lines. The first and the third line rhyme. The middle line rhymes with first line of the next stanza.”

“I don’t get it,” Meg said.

“I want a cupcake,” Tyson announced.

“Face and place rhyme,” I told Meg. “The middle line ends with ascend. That tells us that when we find the next stanza, we’ll know it’s correct if the first line and third lines rhyme with ascend. Terza rima is like an endless paper chain of stanzas, all linked together.”

Meg frowned. “But there isn’t a next stanza.”

“Not here,” I agreed. “Which means it must be somewhere out there….” I waved vaguely to the east. “We’re on a scavenger hunt for more stanzas. This is just the starting point.”

“Hmph.”

As always, Meg had summarized our predicament perfectly. It was very much hmph. I also did not like the fact that our new prophecy’s rhyme scheme had been invented to describe a descent into hell.

“‘The tower of Nero,’” Ella said, repositioning her balloon display. “New York, I bet. Yep.”

I suppressed a whimper.

The harpy was right. We would need to return to where my problems began—Manhattan, where the gleaming Triumvirate headquarters rose from downtown. After that, I would have to face the beast who had usurped my place. I suspected that line didn’t mean Nero’s alter ego, the Beast, but the actual beast Python, my ancient enemy. How I could reach him in his lair at Delphi, much less defeat him, I had no idea.

“New York.” Meg clenched her jaw.

I knew this would be the worst of homecomings for her, back to her stepfather’s house of horrors, where she’d been emotionally abused for years. I wished I could spare her the pain, but I suspected she’d always known this day would come, and like most of the pain she had gone through, there was no choice but to…well, go through it.

“Okay,” she said, her voice resolute. “How do we get there?”

“Oh! Oh!” Tyson raised his hand. His mouth was coated in cupcake frosting. “I would take a rocket ship!”

I stared at him. “Do you have a rocket ship?”

His expression deflated. “No.”

I looked out the bookstore’s picture windows. In the distance, the sun rose over Mount Diablo. Our journey of thousands of miles could not begin with a rocket ship, so we’d have to find another way. Horses? Eagles? A self-driving car that was programmed not to fly off highway overpasses? We’d have to trust in the gods for some good luck. (Insert HA-HA-HA-HA-HA-HA-HA-HA-HA-HA here.) And maybe, if we were very fortunate, we could at least call on our old friends at Camp Half-Blood once we returned to New York. That thought gave me courage.

“Come on, Meg,” I said. “We’ve got a lot of miles to cover. We need to find a new ride.”

ab urbe condita Latin for from the founding of the city. For a time, Romans used the acronym AUC to mark the years since the founding of Rome.

Achilles a Greek hero of the Trojan War; a nearly invulnerable warrior who slayed the Trojan hero Hector outside the walls of Troy and then dragged his corpse behind his chariot

Aphrodite the Greek goddess of love and beauty. Roman form: Venus

Ares the Greek god of war; the son of Zeus and Hera, and half brother to Athena. Roman form: Mars

Argentum Latin for silver; the name of one of Reyna’s two automaton greyhounds that can detect lying

Argo II a flying trireme built by the Hephaestus cabin at Camp Half-Blood to take the demigods of the Prophecy of Seven to Greece

Artemis the Greek goddess of the hunt and the moon; the daughter of Zeus and Leto, and the twin of Apollo. Roman form: Diana

Asclepius the god of medicine; son of Apollo; his temple was the healing center of ancient Greece

Athena the Greek goddess of wisdom. Roman form: Minerva

aura (aurae, pl.) wind spirit

Aurum Latin for gold; the name of one of Reyna’s two automaton greyhounds that can detect lying

ave Latin for hail, a Roman greeting

Bacchus the Roman god of wine and revelry; son of Jupiter. Greek form: Dionysus

ballista (ballistae, pl.) a Roman missile siege weapon that launches a large projectile at a distant target

Bellona a Roman goddess of war; daughter of Jupiter and Juno

Benito Mussolini an Italian politician who became the leader of the National Fascist Party, a paramilitary organization. He ruled Italy from 1922 to 1943, first as a prime minister and then as a dictator.

blemmyae a tribe of headless people with faces in their chests

Britomartis the Greek goddess of hunting and fishing nets; her sacred animal is the griffin

Burning Maze a magical, puzzle-filled underground labyrinth in Southern California controlled by the Roman emperor Caligula and Medea, a Greek sorceress

cacaseca dried poop

Caldecott Tunnel a four-lane highway that cuts through the Berkeley Hills and connects Oakland and Orinda, California. It contains a secret middle tunnel, guarded by Roman soldiers, that leads to Camp Jupiter.

Caligula the nickname of the third of Rome’s emperors, Gaius Julius Caesar Augustus Germanicus, infamous for his cruelty and carnage during the four years he ruled, from 37 to 41 CE; he was assassinated by his own guard