“We talked with Sherman and Malcolm,” Kayla told me. “We’ll be on standby.”

“If there is any chance we can help,” Austin said, “we’ll be ready to roll at a moment’s notice.”

Words were not sufficient to thank them, but I hope they saw the gratitude in my teary, bruised, acne-pocked face.

That night we had the usual singalong at the campfire. No one mentioned our quest. No one offered a going-away good-luck speech. The first-time campers were still so new to the demigod experience, so amazed by it all, I doubted they would even notice we were gone. Perhaps that was for the best.

They didn’t need to know how much was at stake: not just the burning of New York, but whether the Oracle of Delphi would ever be able to give them prophecies and offer them quests, or whether the future would be controlled and predetermined by an evil emperor and a giant reptile.

If I failed, these young demigods would grow up in a world where Nero’s tyranny was the norm and there were only eleven Olympians.

I tried to shove those thoughts to the back of my mind. Austin and I played a duet for saxophone and guitar. Then Kayla joined us to lead the camp in a rousing version of “The Wheels on the Chariot Go ’Round and ’Round.” We roasted marshmallows, and Meg and I tried to enjoy our final hours among our friends.

Small mercies: that night I had no dreams.

At dawn, Will shook me awake. He and Nico had returned from wherever they had been “gathering supplies,” but he didn’t want to talk about it.

Together, he and I met Meg and Nico on the road along the far side of Half-Blood Hill, where the camp’s shuttle bus waited to take us to Rachel Elizabeth Dare’s house in Brooklyn, and—one way or another—the final few days of my mortal life.

BROOKLYN.

Normally, the greatest dangers there are congested traffic, expensive poke bowls, and not enough tables at the local coffee shops for all the aspiring screenwriters. That morning, however, I could tell that our shuttle driver, Argus the giant, was keeping his eyes open for trouble.

This was a big deal for Argus, since he had a hundred sets of eyes all over his body. (I had not actually counted them, nor had I asked if he ever got black eyes on his posterior from sitting too long.)

As we drove down Flushing Avenue, his blue peepers blinked and twitched along his arms, around his neck, and on his cheeks and chin, trying to look in every direction at once.

Clearly, he sensed that something was wrong. I felt it, too. There was an electric heaviness in the air, like just before Zeus hurled a massive lightning bolt or Beyoncé dropped a new album. The world was holding its breath.

Argus pulled over a block from the Dare house as if he feared to get any closer.

The harbor-front area had once been working docklands for local fishermen, if I recalled correctly from the 1800s. Then it had been populated mostly by railyards and factories. You could still see the pilings of decayed piers jutting out of the water. Redbrick shells and concrete smokestacks of old workhouses sat dark and abandoned like temple ruins. One open stretch of railyard was still in operation, with a few heavily graffitied freight cars on the tracks.

But, like the rest of Brooklyn, the neighborhood was rapidly becoming gentrified. Across the street, a building that looked like a onetime machine shop now housed a café promising avocado bagels and pineapple matcha. Two blocks down, cranes loomed from the pit of a construction site. Signs on the fences read HARD HAT AREA, KEEP OUT!, and LUXURY RENTALS COMING SOON! I wondered if the construction workers were required to wear luxury hard hats.

The Dare compound itself was a former industrial warehouse transformed into an ultramodern estate. It occupied an acre of waterfront, making it approximately five billion times larger than the average New York City home. The facade was concrete and steel—like a combination art museum and bombproof bunker.

I had never met Mr. Dare, the real-estate mogul, but I felt I didn’t need to. I understood gods and their palaces. Mr. Dare was operating along the same principles: Look at me, look at my massive pad, spread word of my greatness. You may leave your burnt offerings on the welcome mat.

As soon as we were out of the van, Argus floored the accelerator. He sped off in a cloud of exhaust and premium gravel.

Will and Nico exchanged looks.

“I guess he figured we won’t need a ride back,” Will said.

“We won’t,” Nico said darkly. “Come on.”

He led us to the main gates—huge panels of corrugated steel without any obvious opening mechanism or even an intercom. I suppose if you had to ask, you couldn’t afford to go in.

Nico stood there and waited.

Meg cleared her throat. “Uh, so—?”

The gates rolled open of their own accord. Standing before us was Rachel Elizabeth Dare.

Like all great artists, she was barefoot. (Leonardo would simply never put his sandals on.) Her jeans were covered in marker doodles that had gotten more complex and colorful over the years. Her white tank top was splattered with paint. Across her face, competing for attention with her orange freckles, were streaks of what looked like acrylic ultramarine blue. Some of it dotted her red hair like confetti.

“Come in quickly,” she said, as if she’d been expecting us for hours. “The cattle are watching.”

“Yes, I said cattle,” she told me, preempting my question as we walked through the house. “And, no, I’m not crazy. Hi, Meg. Will, Nico. Follow me. We’ve got the place to ourselves.”

This was like saying we had Yankee Stadium to ourselves. Great, I guess, but I wasn’t sure what to do with it.

The mansion was organized around a central atrium—Roman style, looking inward, so peons outside the walls couldn’t ruin your view. But at least the Romans had gardens. Mr. Dare seemed to believe only in concrete, metal, and gravel. His atrium featured a giant stack of iron and stone that was either a brilliant avant-garde sculpture or a pile of leftover building materials.

We followed Rachel down a wide hall of painted cement, then up a floating stairway into the second level, which I would’ve called the living quarters, except that nothing about the mansion felt very alive. Rachel herself seemed small and out of place here, a warm, colorful aberration padding in her bare feet through an architectural mausoleum.

At least her room had floor-to-ceiling windows that overlooked the neighboring railyard and the river beyond. Sunlight flooded in, illuminating the oak floors, the speckled tarps that doubled as throw rugs, several beanbag chairs, some open cans of paint, and massive easels where Rachel had six different canvases going at once. Spread across the back part of the floor was another half-finished painting that Rachel seemed to be working on with drips and splashes à la Jackson Pollock. Shoved in one corner were a refrigerator and a simple futon, as if eating and sleeping were complete afterthoughts for her.

“Wow.” Will moved to the windows to soak up the view and the sunshine.

Meg made a beeline for the refrigerator.

Nico drifted to the easels. “These are amazing.” He traced the air, following the swirls of Rachel’s paint across the canvas.

“Eh, thanks,” Rachel said absently. “Just warm-ups, really.”

They looked more like full aerobic workouts to me—huge, aggressive brushstrokes, thick wedges of color applied with a mason’s trowel, splashes so large she must have swung an entire can of paint to apply them. At first glance, the works appeared to be abstract. Then I stepped back, and the shapes resolved into scenes.