Finally, we reached Santa Barbara, and I saw why Caligula might like the place.

If I squinted, I could imagine I was back in the Roman resort town of Baiae. The curve of the coastline was almost the same—as well as the golden beaches, the hills dotted with upscale stucco and red-tiled homes, the pleasure craft moored in the harbor. The locals even had the same sunbaked, pleasantly dazed expressions, as if they were biding their time between morning surf sessions and afternoon golf.

The biggest difference: Mount Vesuvius did not rise in the distance. But I had a feeling another presence loomed over this lovely little town—just as dangerous and volcanic.

“He’ll be here,” I said, as we parked the van on Cabrillo Boulevard.

Piper arched her eyebrows. “Are you sensing a disturbance in the Force?”

“Please,” I muttered. “I’m sensing my usual bad luck. In a place this harmless-looking, there’s no way we will not find trouble.”

We spent the afternoon canvassing the Santa Barbara waterfront, from the East Beach to the breakwater jetties. We disrupted a flock of pelicans in the saltwater marsh. We woke some napping sea lions on the fishing dock. We jostled through roving hordes of tourists on Stearns Wharf. In the harbor, we found a virtual forest of single-mast boats, along with some luxury yachts, but none seemed large or gaudy enough for a Roman emperor.

Jason even flew over the water for aerial reconnaissance. When he came back, he reported no suspicious vessels on the horizon.

“Were you on your horse, Tempest, just then?” Meg asked. “I couldn’t tell.”

Jason smiled. “Nah, I don’t call Tempest unless it’s an emergency. I was just flying around on my own, manipulating the wind.”

Meg pouted, considering the pockets of her gardening belt. “I can summon yams.”

At last we gave up searching and grabbed a table at a beachside café. The grilled fish tacos were worthy of an ode by the Muse Euterpe herself.

“I don’t mind giving up,” I admitted, spooning some spicy seviche into my mouth, “if it comes with dinner.”

“This is just a break,” Meg warned. “Don’t get comfortable.”

I wished she hadn’t phrased that as an order. It made it difficult for me to sit still for the rest of my meal.

We sat at the café, enjoying the breeze, the food, and the iced tea until the sun dipped to the horizon, turning the sky Camp Half-Blood orange. I allowed myself to hope that I’d been mistaken about Caligula’s presence. We’d come here in vain. Hooray! I was about to suggest heading back to the van, perhaps finding a hotel so I wouldn’t have to crash in a sleeping bag at the bottom of a desert well again, when Jason rose from our picnic-table bench.

“There.” He pointed out to sea.

The ship seemed to materialize from the sun’s glare, the way my sun chariot used to whenever I pulled into the Stables of Sunset at the end of a long day’s ride. The yacht was a gleaming white monstrosity with five decks above the waterline, its tinted black windows like elongated insect eyes. As with all big ships, it was difficult to judge its size from a distance, but the fact that it had two onboard helicopters, one aft and one forward, plus a small submarine locked in a crane on the starboard side, told me this was not an average pleasure craft. Perhaps there were bigger yachts in the mortal world, but I guessed not many.

“That has to be it,” Piper said. “What now? You think it will dock?”

“Hold on,” Meg said. “Look.”

Another yacht, identical to the first, resolved out of the sunlight about a mile to the south.

“That must be a mirage, right?” Jason asked uneasily. “Or a decoy?”

Meg grunted in dismay, pointing out to sea yet again.

A third yacht shimmered into existence, halfway between the first two.

“This is crazy,” Piper said. “Each one of those boats has to cost millions.”

“Half a billion,” I corrected. “Or more. Caligula was never shy about spending money. He is part of the Triumvirate. They’ve been accumulating wealth for centuries.”

Another yacht popped onto the horizon as if coming out of sunshine warp, then another. Soon there were dozens—a loose armada strung across the mouth of the harbor like a string being fitted on a bow.

“No way.” Piper rubbed her eyes. “This has to be an illusion.”

“It’s not.” My heart sank. I’d seen this sort of display before.

As we watched, the line of super-yachts maneuvered closer together, anchoring themselves stern to bow, forming a glittering, floating blockade from Sycamore Creek all the way to the marina—a mile long at least.

“The Bridge of Boats,” I said. “He’s done it again.”

“Again?” Meg asked.

“Caligula—back in ancient times.” I tried to control the quavering in my voice. “When he was a boy, he received a prophecy. A Roman astrologer told him he had as much chance of becoming emperor as he did of riding a horse across the Bay of Baiae. In other words, it was impossible. But Caligula did become emperor. So he ordered the construction of a fleet of super-yachts”—I gestured feebly at the armada in front of us—“like this. He lined the boats up across the Bay of Baiae, forming a massive bridge. Then he rode across it on his horse. It was the biggest floating construction project ever attempted. Caligula couldn’t even swim. That didn’t faze him. He was determined to thumb his nose at fate.”

Piper steepled her hands over her mouth. “The mortals have to see this, right? He can’t just cut off all boat traffic in and out of the harbor.”

“Oh, the mortals notice,” I said. “Look.”

Smaller boats began to gather around the yachts, like flies drawn to a sumptuous feast. I spotted two Coast Guard vessels, several local police boats, and dozens of inflatable dinghies with outboard motors, manned by dark-clad men with guns—the emperor’s private security, I guessed.

“They’re helping,” Meg murmured, a hard edge to her voice. “Even Nero never…He paid off the police, had lots of mercenaries, but he never showed off this much.”

Jason gripped the hilt of his gladius. “Where do we even start? How do we find Caligula in all of that?”

I didn’t want to find Caligula at all. I wanted to run. The idea of death, permanent death with five whole letters and a d at the beginning, suddenly seemed very close. But I could feel my friends’ confidence wavering. They needed a plan, not a screaming, panicking Lester.

I pointed toward the center of the floating bridge. “We start in the middle—the weakest point of a chain.”

JASON Grace ruined that perfectly good line.

As we tromped toward the surf, he sidled up next to me and murmured, “It’s not true, you know. The middle of a chain has the same tensile strength as everywhere else, assuming force is applied equally along the links.”

I sighed. “Are you making up for missing your physics lecture? You know what I meant!”

“I actually don’t,” he said. “Why attack in the middle?”

“Because…I don’t know!” I said. “They won’t be expecting it?”