From the window of the plane, the last I saw of Piper and Leo, Coach and Mellie, they were huddled on the tarmac, plotting their journey east with their bronze dragon and their yellow Pinto.

Meanwhile, we taxied down the runway in our private jet. We rumbled into the sky—heading for Camp Jupiter and a rendezvous with Reyna, the daughter of Bellona.

I didn’t know how I would find Tarquin’s tomb, or who the soundless god was supposed to be. I didn’t know how we would stop Caligula from attacking the damaged Roman camp. But none of that bothered me as much as what had happened to us already—so many lives destroyed, a hero’s coffin rattling in the cargo hold, three emperors who were all still alive, ready to wreak more havoc on everyone and everything I cared about.

I found myself crying.

It was ridiculous. Gods don’t cry. But as I looked at Jason’s diorama in the seat next to me, all I could think about was that he would never get to see his carefully labeled plans finished. As I held my ukulele, I could only picture Crest playing his last chord with broken fingers.

“Hey.” Meg turned in the seat in front of me. Despite her usual cat-eye glasses and preschool-colored outfit (somehow mended, yet again, by the magic of the ever-patient dryads), Meg sounded more grown-up today. Surer of herself. “We’re going to make everything right.”

I shook my head miserably. “What does that even mean? Caligula is heading north. Nero is still out there. We’ve faced three emperors, and defeated none of them. And Python—”

She bopped me on the nose, much harder than she had Baby Chuck.

“Ow!”

“Got your attention?”

“I—Yes.”

“Then listen: You will get to the Tiber alive. You will start to jive. That’s what the prophecy said back in Indiana, right? It will make sense once we get there. You’re going to beat the Triumvirate.”

I blinked. “Is that an order?”

“It’s a promise.”

I wished she hadn’t put it that way. I could almost hear the goddess Styx laughing, her voice echoing from the cold cargo hold where the son of Jupiter now rested in his coffin.

The thought made me angry. Meg was right. I would defeat the emperors. I would free Delphi from Python’s grasp. I would not allow those who had sacrificed themselves to do so for nothing.

Perhaps this quest had ended on a suspended fourth chord. We still had much to do.

But from now on, I would be more than Lester. I would be more than an observer.

I would be Apollo.

I would remember.

aeithales ancient Greek for evergreen

Aeneas a prince of Troy and reputed ancestor of the Romans; the hero of Virgil’s epic the Aeneid

Alexander the Great a king of the ancient Greek kingdom of Macedon from 336 to 323 BCE; he united the Greek city-states and conquered Persia

ambrosia the food of the gods; it gives immortality to whoever consumes it; demigods can eat it in small doses to heal their injuries

Aphrodite Greek goddess of love and beauty; Roman form: Venus

arbutus any shrub or tree in the heath family with white or pink flowers and red or orange berries

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

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

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

Athena the Greek goddess of wisdom

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

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

cabrito roasted or stewed kid goat meat

caligae (caliga, sing.) Roman military boots

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

Camp Half-Blood the training ground for Greek demigods, located in Long Island, New York

Camp Jupiter the training ground for Roman demigods, located in California, between the Oakland Hills and the Berkeley Hills

Cave of Trophonius a deep chasm, home to the Oracle Trophonius

Celestial bronze a powerful magical metal used to create weapons wielded by Greek gods and their demigod children

Chicago Black Sox eight members of the Chicago White Sox, a Major League Baseball team, accused of intentionally losing the 1919 World Series against the Cincinnati Reds in exchange for money

Claudius Roman emperor from 41 to 54 CE, succeeding Caligula, his nephew

Commodus Lucius Aurelius Commodus was the son of Roman Emperor Marcus Aurelius; he became co-emperor when he was sixteen and emperor at eighteen, when his father died; he ruled from 177 to 192 CE and was megalomaniacal and corrupt; he considered himself the New Hercules and enjoyed killing animals and fighting gladiators at the Colosseum

Cyclops (Cyclopes, pl.) a member of a primordial race of giants, each with a single eye in the middle of his or her forehead

Daedalus a skilled craftsman who created the Labyrinth on Crete in which the Minotaur (part man, part bull) was kept

Daphne a beautiful naiad who attracted Apollo’s attention; she transformed into a laurel tree in order to escape him

Delos a Greek island in the Aegean Sea near Mykonos; birthplace of Apollo

Demeter the Greek goddess of agriculture; a daughter of the Titans Rhea and Kronos

denarius (denarii, pl.) a unit of Roman currency

Dionysus Greek god of wine and revelry; the son of Zeus

Doors of Death the doorway to the House of Hades, located in Tartarus; the doors have two sides—one in the mortal world, and one in the Underworld

dryad a spirit (usually female) associated with a certain tree

Edesia Roman goddess of banquets

Edsel a car produced by Ford from 1958 to 1960; it was a big flop

Elysium the paradise to which Greek heroes were sent when the gods gave them immortality

empousa a winged bloodsucking monster, daughter of the goddess Hecate

Enceladus a giant, son of Gaea and Ouranos, who was the primary adversary of the goddess Athena during the War of the Giants

Erymanthian Boar a giant wild boar that terrorized people on the island of Erymanthos until Hercules subdued it in the third of his twelve labors

Erythraean Sibyl a prophetess who presided over Apollo’s Oracle at Erythrae in Ionia

Euterpe Greek goddess of lyric poetry; one of the Nine Muses; daughter of Zeus and Mnemosyne

Feronia the Roman goddess of wildlife, also associated with fertility, health and abundance

Furies goddesses of vengeance

Gaea the Greek earth goddess; wife of Ouranos; mother of the Titans, giants, Cyclopes, and other monsters

Germanicus adoptee of the Roman emperor Tiberius; became a prominent general of the Roman empire, known for his successful campaigns in Germania; father of Caligula

gladius a stabbing sword; the primary weapon of Roman foot soldiers

Golden Fleece the much-coveted fleece of the gold-haired winged ram, which was held in Colchis by King Aeëtes and guarded by a dragon until Jason and the Argonauts retrieved it