Grover steered us toward the largest of the brick cylinders. Judging from its size and position in the center of the ruins, I guessed it must have once been the central support column for the structure. At ground level, rectangular openings ringed the circumference like medieval castle windows. We dragged Meg through one of these and found ourselves in a space very much like the well where we’d fought the strixes.

The top was open to the sky. A spiral ramp led downward, but fortunately only twenty feet before reaching the bottom. In the center of the dirt floor, like the hole in a giant donut, glittered a dark blue pool, cooling the air and making the space feel comfortable and welcoming. Around the pool lay a ring of sleeping bags. Blooming cacti overflowed from alcoves built into the walls.

The Cistern was not a fancy structure—nothing like the dining pavilion at Camp Half-Blood, or the Waystation in Indiana—but inside it I immediately felt better, safer. I understood what Grover had been talking about. This place resonated with soothing energy.

We got Meg to the bottom of the ramp without tripping and falling, which I considered a major accomplishment. We set her down on one of the sleeping bags, then Grover scanned the room.

“Mellie?” he called. “Gleeson? Are you guys here?”

The name Gleeson sounded vaguely familiar to me, but, as usual, I couldn’t place it.

No chlorophyll bubbles popped from the plants. Meg turned on her side and muttered in her sleep…something about Peaches. Then, at the edge of the pond, wisps of white fog began to gather. They fused into the shape of a petite woman in a silvery dress. Her dark hair floated around her as if she were underwater, revealing her slightly pointed ears. In a sling over one shoulder she held a sleeping baby perhaps seven months old, with hooved feet and tiny goat horns on his head. His fat cheek was squished against his mother’s clavicle. His mouth was a veritable cornucopia of drool.

The cloud nymph (for surely that’s what she was) smiled at Grover. Her brown eyes were bloodshot from lack of sleep. She held one finger to her lips, indicating that she’d rather not wake the baby. I couldn’t blame her. Satyr babies at that age are loud and rambunctious, and can teethe their way through several metal cans a day.

Grover whispered, “Mellie, you made it!”

“Grover, dear.” She looked down at the sleeping form of Meg, then tilted her head at me. “Are you…Are you him?”

“If you mean Apollo,” I said, “I’m afraid so.”

Mellie pursed her lips. “I’d heard rumors, but I didn’t believe them. You poor thing. How are you holding up?”

In times past, I would have scoffed at any nymph who dared to call me poor thing. Of course, few nymphs would have shown me such consideration. Usually they were too busy running away from me. Now, Mellie’s show of concern caused a lump to form in my throat. I was tempted to rest my head on her other shoulder and sob out my troubles.

“I—I’m fine,” I managed. “Thank you.”

“And your sleeping friend here?” she asked.

“Just exhausted, I think.” Though I wondered if that was the whole story with Meg. “Aloe Vera said she would be along in a few minutes to care for her.”

Mellie looked worried. “All right. I’ll make sure Aloe doesn’t overdo it.”

“Overdo it?”

Grover coughed. “Where’s Gleeson?”

Mellie scanned the room, as if just realizing this Gleeson person was not present. “I don’t know. As soon as we got here, I went dormant for the day. He said he was going into town to pick up some camping supplies. What time is it?”

“After sunset,” Grover said.

“He should’ve been back by now.” Mellie’s form shimmered with agitation, becoming so hazy I was afraid the baby might fall right through her body.

“Gleeson is your husband?” I guessed. “A satyr?”

“Yes, Gleeson Hedge,” Mellie said.

I remembered him then, vaguely—the satyr who had sailed with the demigod heroes of the Argo II. “Do you know where he went?”

“We passed an army-surplus store as we drove in, down the hill. He loves army-surplus stores.” Mellie turned to Grover. “He may have just gotten distracted, but…I don’t suppose you could go check on him?”

At that moment, I realized just how exhausted Grover Underwood must be. His eyes were even redder than Mellie’s. His shoulders drooped. His reed pipes dangled listlessly from his neck. Unlike Meg and me, he hadn’t slept since last night in the Labyrinth. He’d used the cry of Pan, gotten us to safety, then spent all day guarding us, waiting for the dryads to wake up. Now he was being asked to make another excursion to check on Gleeson Hedge.

Still, he mustered a smile. “Sure thing, Mellie.”

She gave him a peck on the cheek. “You’re the best lord of the Wild ever!”

Grover blushed. “Watch Meg McCaffrey until we get back, would you? Come on, Apollo. Let’s go shopping.”

EVEN after four thousand years, I could still learn important life lessons. For instance: Never go shopping with a satyr.

Finding the store took forever, because Grover kept getting sidetracked. He stopped to chat with a yucca. He gave directions to a family of ground squirrels. He smelled smoke and led us on a chase across the desert until he found a burning cigarette someone had dropped onto the road.

“This is how fires start,” he said, then responsibly disposed of the cigarette butt by eating it.

I didn’t see anything within a mile radius that could have caught fire. I was reasonably sure rocks and dirt were not flammable, but I never argue with people who eat cigarettes. We continued our search for the army-surplus store.

Night fell. The western horizon glowed—not with the usual orange of mortal light pollution, but with the ominous red of a distant inferno. Smoke blotted out the stars. The temperature barely cooled. The air still smelled bitter and wrong.

I remembered the wave of flames that had nearly incinerated us in the Labyrinth. The heat seemed to have had a personality—a resentful malevolence. I could imagine such waves coursing beneath the surface of the desert, washing through the Labyrinth, turning the mortal terrain above into an even more uninhabitable wasteland.

I thought about my dream of the woman in molten chains, standing on a platform above a pool of lava. Despite my fuzzy memories, I was sure that woman was the Erythraean Sibyl, the next Oracle we had to free from the emperors. Something told me she was imprisoned in the very center of…whatever was generating those subterranean fires. I did not relish the idea of finding her.

“Grover,” I said, “in the greenhouse, you mentioned something about search parties?”

He glanced over, swallowing painfully, as if the cigarette butt were still stuck in his throat. “The heartiest satyrs and dryads—they’ve been fanning out across the area for months.” He fixed his eyes on the road. “We don’t have many searchers. With the fires and the heat, the cacti are the only nature spirits that can still manifest. So far, only a few have come back alive. The rest…we don’t know.”

“What are they are searching for?” I asked. “The source of the fires? The emperor? The Oracle?”