“The emperor is better known by his childhood nickname,” I said. “Which he despises, by the way. History remembers him as Caligula.”

DO you know the name Caligula, dear reader?

If not, consider yourself lucky.

All around the Cistern, cactus dryads puffed out their spikes. Mellie’s lower half dissolved into mist. Even Baby Chuck coughed up a piece of Styrofoam.

“Caligula?” Coach Hedge’s eye twitched the same way it had when Mellie threatened to take away his ninja weapons. “Are you sure?”

I wished I wasn’t. I wished I could announce that the third emperor was kindly old Marcus Aurelius, or noble Hadrian, or bumbling Claudius.

But Caligula…

Even for those who knew little about him, the name Caligula conjured the darkest, most depraved images. His reign was bloodier and more infamous than Nero’s, who had grown up in awe of his wicked great-uncle Gaius Julius Caesar Germanicus.

Caligula: a byword for murder, torture, madness, excess. Caligula: the villainous tyrant against whom all other villainous tyrants were measured. Caligula: who had a worse branding problem than the Edsel, the Hindenburg, and the Chicago Black Sox put together.

Grover shuddered. “I’ve always hated that name. What does it mean, anyway? Satyr Killer? Blood Drinker?”

“Booties,” I said.

Joshua’s shaggy olive hair stood straight up, which Meg seemed to find fascinating.

“Booties?” Joshua glanced around the Cistern, perhaps wondering if he’d missed the joke. No one was laughing.

“Yes.” I could still remember how cute little Caligula had looked in his miniature legionnaire’s outfit when he accompanied his father, Germanicus, on military campaigns. Why were sociopaths always so adorable as children?

“His father’s soldiers gave Caligula the nickname when he was a child,” I said. “He wore teeny-weenie legionnaire’s boots, caligae, and they thought that was hysterical. So they called him Caligula—Little Boots, or Baby Shoes, or Booties. Pick your translation.”

Prickly Pear stabbed her fork into her enchiladas. “I don’t care if the guy’s name is Snookums McCuddleFace. How do we beat him and get our lives back to normal?”

The other cacti grumbled and nodded. I was starting to suspect that prickly pears were the natural agitators of the cactus world. Get enough of them together, and they would start a revolution and overthrow the animal kingdom.

“We have to be careful,” I warned. “Caligula is a master at trapping his enemies. The old saying Give them enough rope to hang themselves? That was made for Caligula. He delights in his reputation as a madman, but it’s just a cover. He’s quite sane. He’s also completely amoral, even worse than…”

I stopped myself. I’d been about to say worse than Nero, but how could I make such a claim in front of Meg, whose entire childhood had been poisoned by Nero and his alter ego, the Beast?

Careful, Meg, Nero would always say. Don’t misbehave or you’ll wake the Beast. I love you dearly, but the Beast…Well, I would hate to see you do something wrong and get hurt.

How could I quantify such villainy?

“Anyway,” I said, “Caligula is smart, patient, and paranoid. If this Burning Maze is some elaborate trap, part of some bigger plan of his, it won’t be easy to shut down. And beating him, even finding him, will be a challenge.” I was tempted to add Perhaps we don’t want to find him. Perhaps we should run away.

That wouldn’t work for the dryads. They were rooted, quite literally, to the land in which they grew. Transplants like Reba were rare. Few nature spirits could survive being potted and transported to a new environment. Even if every dryad here managed to flee the fires of Southern California, thousands more would stay and burn.

Grover shuddered. “If half the stuff I’ve heard about Caligula is true…”

He paused, apparently realizing that everyone was watching him, gauging how much they should panic based on Grover’s reactions. I, for one, did not want to be in the middle of a room filled with cacti that were running around screaming.

Fortunately, Grover kept his cool.

“Nobody is unbeatable,” he declared. “Not Titans, giants, or gods—and definitely not some Roman emperor named Booties. This guy is causing Southern California to wither and die. He’s behind the droughts, the heat, the fires. We have to find a way to stop him. Apollo, how did Caligula die the first time?”

I tried to remember. As usual, my mortal hard drive of a brain was shot full of holes, but I seemed to recall a dark tunnel packed with praetorian guards, crowding around the emperor, their knives flashing and glistening with blood.

“His own guards killed him,” I said, “which I’m sure has made him even more paranoid. Macro mentioned that the emperor kept changing his personal guard. First automatons replaced the praetors. Then he changed them again to mercenaries and strixes and…big ears? I don’t know what that means.”

One of the dryads huffed indignantly. I guessed she was Cholla, since she looked like a cholla plant—wispy white hair, a fuzzy white beard, and large paddle-shaped ears covered with bristles. “No decent big-eared person would work for such a villain! What about other weaknesses? The emperor must have some!”

“Yeah!” Coach Hedge chimed in. “Is he scared of goats?”

“Is he allergic to cactus sap?” Aloe Vera asked hopefully.

“Not that I know of,” I said.

The assembled dryads looked disappointed.

“You said you got a prophecy in Indiana?” Joshua asked. “Any clues there?”

His tone was skeptical, which I could understand. A Hoosier prophecy just doesn’t have the same ring to it as a Delphic prophecy.

“I have to find the westward palace,” I said. “Which must mean Caligula’s base.”

“No one knows where that is,” grumbled Pear.

Perhaps it was my imagination, but Mellie and Gleeson seemed to exchange an anxious look. I waited for them to say something else, but they did not.

“Also from the prophecy…” I continued. “I have to wrest from him the crossword speaker’s breath. Meaning, I think, that I have to free the Erythraean Sibyl from his control.”

“Does this Sibyl like crosswords?” Reba asked. “I like crosswords.”

“The Oracle gave her prophecies in the form of word puzzles,” I explained. “Like crosswords. Or acrostics. The prophecy also talks about Grover bringing us here, and a lot of terrible things that will happen at Camp Jupiter in the next few days—”

“The new moon,” Meg muttered. “Coming very soon.”

“Yes.” I tried to contain my annoyance. Meg seemed to want me to be in two places at once, which would have been no problem for Apollo the god. For Lester the human, I could barely manage being in one place at once.

“There’s another line,” Grover remembered. “Walk the path in thine own enemy’s boots? Could that have something to do with Caligula’s booties?”

I imagined my ginormous sixteen-year-old feet crammed into a Roman toddler’s military-issued leather baby shoes. My toes began to throb.

“I hope not,” I said. “But if we could free the Sibyl from the maze, I’m sure she would help us. I’d like to have more guidance before I charge off to confront Caligula in person.”