“Tell me your story,” Aphros said.

Leo hesitated, but not for long. Somehow he sensed that he should tell the truth. He started at the beginning—how Hera had been his babysitter and placed him in the flames; how his mother had died because of Gaea, who had identified Leo as a future enemy. He talked about how he had spent his childhood bouncing around in foster homes, until he and Jason and Piper had been taken to Camp Half-Blood. He explained the Prophecy of Seven, the building of the Argo II, and their quest to reach Greece and defeat the giants before Gaea woke.

As he talked, Aphros drew some wicked-looking metal spikes from his belt. Leo was afraid he had said something wrong, but Aphros pulled some seaweed yarn from his pouch and started knitting. “Go on,” he urged. “Don’t stop.”

By the time Leo had explained the eidolons, the problem with the Romans, and all the troubles the Argo II had encountered crossing the United States and embarking from Charleston, Aphros had knitted a complete baby bonnet.

Leo waited while the fish centaur put away his supplies. Aphros’s lobster-claw horns kept swimming around in his thick hair, and Leo had to resist the urge to try to rescue them.

“Very well,” Aphros said. “I believe you.”

“As simple as that?”

“I am quite good at discerning lies. I hear none from you. Your story also fits with what Hazel Levesque told us.”

“Is she—?”

“Of course,” Aphros said. “She’s fine.” He put his fingers to his mouth and whistled, which sounded strange underwater—like a dolphin screaming. “My people will bring her here shortly. You must understand…our location is a carefully guarded secret. You and your friends showed up in a warship, pursued by one of Keto’s sea monsters. We did not know whose side you were on.”

“Is the ship all right?”

“Damaged,” Aphros said, “but not terribly. The skolopendra withdrew after it got a mouthful of fire. Nice touch.”

“Thank you. Skolopendra? Never heard of it.”

“Consider yourself lucky. They are nasty creatures. Keto must really hate you. At any rate, we rescued you and the other two from the creature’s tentacles as it retreated into the deep. Your friends are still above, searching for you; but we have obscured their vision. We had to be sure you were not a threat. Otherwise, we would have had to…take measures.”

Leo gulped. He was pretty sure taking measures did not mean baking extra brownies. And if these guys were so powerful that they could keep their camp hidden from Percy, who had all those Poseidonish water powers, they were not fish dudes to mess with. “So…we can go?”

“Soon,” Aphros promised. “I must check with Bythos. When he is done talking with your friend Gank—”

“Frank.”

“Frank. When they are done, we will send you back to your ship. And we may have some warnings for you.”

“Warnings?”

“Ah.” Aphros pointed. Hazel emerged from the kelp forest, escorted by two vicious-looking mermaids, who were baring their fangs and hissing. Leo thought Hazel might be in danger. Then he saw she was completely at ease, grinning and talking with her escorts, and Leo realized that the mermaids were laughing.

“Leo!” Hazel paddled toward him. “Isn’t this place amazing?”

They were left alone at the ridge, which must have meant Aphros really did trust them. While the centaur and the mermaids went off to fetch Frank, Leo and Hazel floated above the hill and gazed down at the underwater camp.

Hazel told him how the mermaids had warmed up to her right away. Aphros and Bythos had been fascinated by her story, as they had never met a child of Pluto before. On top of that, they had heard many legends about the horse Arion, and they were amazed that Hazel had befriended him.

Hazel had promised to visit again with Arion. The mermaids had written their phone numbers in waterproof ink on Hazel’s arm so that she could keep in touch. Leo didn’t even want to ask how mermaids got cell-phone coverage in the middle of the Atlantic.

As Hazel talked, her hair floated around her face in a cloud—like brown earth and gold dust in a miner’s pan. She looked very sure of herself and very beautiful—not at all like the shy, nervous girl in that New Orleans schoolyard with her smashed canvas lunch bag at her feet.

“We didn’t get to talk,” Leo said. He was reluctant to bring up the subject, but he knew this might be their only chance to be alone. “I mean about Sammy.”

Her smile faded. “I know…I just need some time to let it sink in. It’s strange to think that you and he…”

She didn’t need to finish the thought. Leo knew exactly how strange it was.

“I’m not sure I can explain this to Frank,” she added. “About you and me holding hands.”

She wouldn’t meet Leo’s eyes. Down in the valley, the Cyclopes work crew cheered as the temple roof was set in place.

“I talked to him,” Leo said. “I told him I wasn’t trying to…you know. Make trouble between you two.”

“Oh. Good.”

Did she sound disappointed? Leo wasn’t sure, and he wasn’t sure he wanted to know.

“Frank, um, seemed pretty freaked out when I summoned fire.” Leo explained what had happened in the cave.

Hazel looked stunned. “Oh, no. That would terrify him.”

Her hand went to her denim jacket, like she was checking for something in the inside pocket. She always wore that jacket, or some sort of overshirt, even when it was hot outside. Leo had assumed that she did it out of modesty, or because it was better for horseback riding, like a motorcycle jacket. Now he began to wonder.

His brain shifted into high gear. He remembered what Frank had said about his weakness…a piece of firewood. He thought about why this kid would have a fear of fire, and why Hazel would be so attuned to those feelings. Leo thought about some of the stories he’d heard at Camp Half-Blood. For obvious reasons, he tended to pay attention to legends about fire. Now he remembered one he hadn’t thought about in months.

“There was an old legend about a hero,” he recalled. “His lifeline was tied to a stick in a fireplace, and when that piece of wood burned up…”

Hazel’s expression turned dark. Leo knew he’d struck on the truth.

“Frank has that problem,” he guessed. “And the piece of firewood…” He pointed at Hazel’s jacket. “He gave it to you for safekeeping?”

“Leo, please don’t…I can’t talk about it.”

Leo’s instincts as a mechanic kicked in. He started thinking about the properties of wood and the corrosiveness of salt water. “Is the firewood okay in the ocean like this? Does the layer of air around you protect it?”

“It’s fine,” Hazel said. “The wood didn’t even get wet. Besides, it’s wrapped up in several layers of cloth and plastic and—” She bit her lip in frustration. “And I’m not supposed to talk about it! Leo, the point is if Frank seems afraid of you, or uneasy, you’ve got to understand…”

Leo was glad he was floating, because he probably would’ve been too dizzy to stand. He imagined being in Frank’s position, his life so fragile, it literally could burn up at any time. He imagined how much trust it would take to give his lifeline—his entire fate—to another person.

Frank had chosen Hazel, obviously. So when he had seen Leo—a guy who could summon fire at will—moving in on his girl…

Leo shuddered. No wonder Frank didn’t like him. And suddenly Frank’s ability to turn into a bunch of different animals didn’t seem so awesome—not if it came with a big catch like that.

Leo thought about his least favorite line in the Prophecy of Seven: To storm or fire the world must fall. For a long time, he’d figured that Jason or Percy stood for storm—maybe both of them together. Leo was the fire guy. Nobody said that, but it was pretty clear. Leo was one of the wild cards. If he did the wrong thing, the world could fall. No…it must fall. Leo wondered if Frank and his firewood had something to do with that line. Leo had already made some epic mistakes. It would be so easy for him to accidentally send Frank Zhang up in flames.

“There you are!” Bythos’s voice made Leo flinch.

Bythos and Aphros floated over with Frank between them, looking pale but okay. Frank studied Hazel and Leo carefully, as if trying to read what they’d been talking about.

“You are free to go,” Bythos said. He opened his saddlebags and returned their confiscated supplies. Leo had never been so glad to fit his tool belt around his waist.

“Tell Percy Jackson not to worry,” Aphros said. “We have understood your story about the imprisoned sea creatures in Atlanta. Keto and Phorcys must be stopped. We will send a quest of mer-heroes to defeat them and free their captives. Perhaps Cyrus?”

“Or Bill,” Bythos offered.

“Yes! Bill would be perfect,” Aphros agreed. “At any rate, we are grateful that Percy brought this to our attention.”

“You should talk to him in person,” Leo suggested. “I mean, son of Poseidon, and all.”

Both fish-centaurs shook their heads solemnly. “Sometimes it is best not to interact with Poseidon’s brood,” Aphros said. “We are friendly with the sea god, of course; but the politics of undersea deities is…complicated. And we value our independence. Nevertheless, tell Percy thank you. We will do what we can to speed you safely across the Atlantic without further interference from Keto’s monsters, but be warned: in the ancient sea, the Mare Nostrum, more dangers await.”

Frank sighed. “Naturally.”

Bythos clapped the big guy on the shoulder. “You will be fine, Frank Zhang. Keep practicing those sea life transformations. The koi fish is good, but try for a Portuguese man-of-war. Remember what I showed you. It’s all in the breathing.”

Frank looked mortally embarrassed. Leo bit his lip, determined not to smile.

“And you, Hazel,” Aphros said, “come visit again, and bring that horse of yours! I know you are concerned about the time you lost, spending the night in our realm. You are worried about your brother, Nico.…”

Hazel gripped her cavalry sword. “Is he—do you know where he is?”

Aphros shook his head. “Not exactly. But when you get closer, you should be able to sense his presence. Never fear! You must reach Rome the day after tomorrow if you are to save him, but there is still time. And you must save him.”

“Yes,” Bythos agreed. “He will be essential for your journey. I am not sure how, but I sense it is true.”

Aphros planted his hand on Leo’s shoulder. “As for you, Leo Valdez, stay close to Hazel and Frank when you reach Rome. I sense they will face…ah, mechanical difficulties that only you can overcome.”

“Mechanical difficulties?” Leo asked.

Aphros smiled as if that was great news. “And I have gifts for you, the brave navigator of the Argo II!”