Chapter Text
For five long years, Luke Castellan had nurtured a very specific obsession.
From the exact day he first set foot in Camp Half-Blood at age fourteen—fleeing a broken mother and bearing the weight of a destiny he already despised—a recurring rumor had echoed in his ears. Camp Half-Blood gossip traveled faster than Hermes’s winged sandals, and the story was always the same, no matter how many times the details changed: Poseidon had broken the pact first. There was a girl. Two years older than Thalia Grace. Hidden away in the deepest depths of the Atlantis palace, trained by royal tridents—a potential deity ready to either unleash the end of the world or save it.
Her name was Perseidas. The Princess of the Sea.
To nineteen-year-old Luke, the leader of a silent rebellion sworn to destroy Olympus, Perseidas wasn’t an urban legend; she was the perfect chess piece. A demigod his own age, powerful, and likely resentful for having spent her entire life hidden underwater like her father’s shameful secret. Face to face, Luke was certain he could mold her. He would offer her freedom, a side where she wouldn't have to hide, and together, they would burn Olympus to the ground.
Because of this, planning her extraction had been meticulous. It had taken him weeks to contact a sea monster stupid enough not to ask questions and strong enough to swim into the abyss and bring the girl back to him.
That night, the wind howled fiercely along the Long Island sound. The camp's woods were dark and silent, broken only by the crunch of leaves beneath Luke’s boots as he slipped past the boundaries, near the creek.
A massive, dripping silhouette emerged from the shadows of the trees. It was a sea demon—a creature with shark-like skin, razor-sharp claws, and a face only a Telkhine mother could love. It came shuffling forward, leaving a trail of seaweed and saltwater in its wake.
Luke stopped, crossing his arms over his chest. His face tightened into a smug, self-assured smirk. The moment had arrived. His secret weapon was here.
"Do you have her?" Luke asked, keeping his voice low and commanding.
The monster nodded, letting out a guttural gurgle. With agonizing slowness, it extended its massive, scaly claws forward.
Luke blinked. He had expected to see an imposing warrior, perhaps bound in kelp ropes, or at least a furious teenager with Poseidon’s green eyes flashing. Instead, the monster held a bundle. A pink cotton blanket patterned with seahorses, and rather damp.
From the blanket poked a tiny fist, no bigger than a walnut, waving weakly in the air. A small, high-pitched, and completely harmless whimper escaped the bundle.
Luke froze. He looked at the blanket. He looked at the monster’s fish-face. He looked back at the blanket.
"What is this?" Luke’s voice lost all its authoritative, rebel-leader gravity, replaced by a tone of pure utter bewilderment.
"The girl," the monster hissed, its voice sounding like gravel being dragged by the tide. "The princess Perseidas."
The blood rushed to Luke's head. He felt a vein in his forehead begin to throb violently.
"You absolute idiot!" he snapped in a furious whisper, stepping forward and pointing at the bundle. "I told you to bring the girl, Perseidas! A girl! Nineteen years old! Do you see how tall I am?!" Luke thamped his own chest in sheer indignation. "This is what someone who is nineteen looks like, at the bare minimum! This is a bloody tadpole!"
The monster blinked its large, black eyes, visibly confused by the demigod's lack of gratitude.
"It is the girl," the creature insisted, thrusting the bundle a bit closer to him. "Born a month ago."
"A month ago?!" Luke felt as though the entire universe was laughing at him. Five years of rumors for this? "Are you telling me that Poseidon’s great secret, the forbidden firstborn, the destroyer of Olympus... wears diapers?"
"She smells of the sea," the monster argued, as if that explained everything. "Royal blood. It is her."
Before Luke could demand that it return to the ocean and bring him an adult, the sharp, loud snapping of dry twigs a few yards away made him freeze. The woods' night patrol shift. He recognized the heavy, metallic tread in the distance. Clarisse La Rue.
"Someone's out there!" the daughter of Ares's voice boomed through the trees.
Panic—a purely mundane, non-mythological panic—seized Luke. If they found a sea monster with him, his cover would blow into a thousand pieces.
"Get out of here!" he hissed at the monster, giving it a rough, hydrophobic shove. "Go! Back to the water!"
The sea demon, terrified by Luke’s tone, dumped the bundle straight into the demigod's arms before spinning around and scrambling back toward the creek, vanishing with a loud splash.
Luke was left standing in the dark, suddenly holding a damp, seven-pound package that was beginning to wriggle. His sword, Backbiter—a weapon designed to reap divine souls—hung from his belt, and there he was, holding a creature that smelled of baby powder and saltwater.
Flashlight beams pierced through the trees. Clarisse emerged from the brush, her electric spear raised and shield ready, followed by a couple of kids from the Hermes cabin.
"Hold it right there! I heard noises from—" Clarisse stopped dead in her tracks as she shone her flashlight directly into Luke’s face. Then, she lowered the beam toward his arms. "Luke? What the hell...?"
Luke, who usually had a cold, calculated answer for any unexpected turn of events, went completely blank. The baby in his arms let out a noisy yawn.
The son of Hermes looked at Clarisse, then looked down at the baby, and with the straightest face he could muster, blurts out the first thing that came to mind:
"Apparently... monsters are kidnapping infants now."
Clarisse frowned, taking three steps closer and lowering her spear to inspect the creature.
"A baby? Seriously? Monsters crawled out of the water just to steal a baby? Talk about hitting a new low. Is she a mortal?"
"She must be the daughter of some tourist at the North Shore beaches," Luke lied without blinking. "I intercepted a Telkhine just as it was coming out of the surf with her. The damn thing fled the second I drew my sword."
Clarisse stared at the baby, her gaze lingering for a moment on the eyes the infant had just opened—eyes the exact color of the sea. Then, she scratched her chin, remembering something.
"Hey... that kid looks strangely familiar," the daughter of Ares grunted, narrowing her eyes. "My dad's Roman counterpart, Mars Ultor, had a daughter recently. He showed her to us because, according to the mortal mother, she carries Greek blood. The kid has eyes that exact same color. Couldn't she be—"
"Don't be ridiculous, Clarisse," Luke interrupted with a smooth, dismissive laugh, cutting off her train of thought. "Your father has plenty of kids in both versions. So many they could probably populate Vatican City, and most of them remain unclaimed because the satyrs can't find them. This is just a poor mortal baby who had the misfortune of crossing paths with a hungry demon."
Clarisse snorted, easily convinced by Luke's logic that her father was a womanizer just like Zeus. As the saying went, if it had a pulse, he'd go after it, and she highly doubted his Roman version was any different.
"Whatever. What are we going to do with her? We can't just leave her in the woods. If Chiron sees her, he's going to start involving the police to look for the mortal parents all over Long Island."
Luke looked down at the baby. Perseidas stared back, shoving her tiny fist into her mouth to chew on it. A much more twisted, amusing, and long-term plan began to take shape in the Hermes cabin leader's mind.
"I'll take care of it," Luke said, flashing Clarisse a reassuring smile. "I'll keep her in the Hermes cabin for tonight. Tomorrow we'll brief Chiron so he can handle the mortal bureaucracy. Get back to your patrol, Clarisse. I've got the mortal covered."
Clarisse rolled her eyes, turned around, and marched back into the woods, muttering under her breath about how the camp was going soft.
Once he was alone, Luke lifted Perseidas up to eye level. The clouds parted, allowing the moonlight to illuminate her face.
"So, Poseidon's daughter turned out to be a baby," Luke whispered with a malicious grin. "Well, no matter. Kronos will be able to use you as his vessel without any resistance."
Luke Castellan’s plan had been perfect. Cold, calculated, and entirely worthy of a son of Hermes playing chess with the very destiny of Olympus.
Of course, that was assuming Camp Half-Blood wasn't a breeding ground for professional gossips.
By seven in the morning, the tale of how the heroic leader of Cabin Eleven had rescued a helpless baby from the clutches of a sea monster had already been distorted about fifteen times. Someone from the night patrol shift had spread the word, and by the time the sun fully rose, demigods were practically trampling each other outside the Hermes cabin just to catch a glimpse of the "miracle of the woods."
Luke hadn't even had time to process his own headache before the Aphrodite girls raided the cabin. Taking advantage of the fact that one of his cabin's rookies had accidentally shrunk part of her wardrobe in the mythical laundry, they confiscated the baby. In less than ten minutes, they had stripped her of the ocean blanket and dressed her in a tiny, neon-orange outfit that read CAMP HALF-BLOOD in bold black letters, paired with denim shorts that fit her ridiculously tight.
By breakfast, baby Perseidas was already the main attraction at the dining pavilion. She was sitting right in the middle of the Hermes table, propped up by a couple of thirteen-year-olds who stared at her as if she were an explosive device, while the girl sucked with unnatural strength from a makeshift baby bottle. She had her brow so deeply furrowed and a scowl so fierce that, if it weren't for the faint scent of sea salt wafting off her, anyone would have sworn she was a daughter of Ares plotting a war crime.
Luke watched the scene from the end of the table, a cup of black coffee cupped between his hands, feeling a growing sensation that control of the situation was slipping through his fingers.
Then, the goblets at the dining pavilion frosted over, and the air filled with the heavy stench of sour wine. Mr. D made his grand entrance onto the head table's platform.
Dionysus didn’t sport his usual mood of bitter apathy; he looked genuinely irritated, which was always a bad sign for the demigods around him. He cleared his throat with a sharp scowl and, without preamble, began the morning announcements.
"Listen up, brats, because I am not going to repeat myself," the wine god grumbled, running a bored hand over his leopard-print shirt. "All water in the camp is strictly forbidden starting this very instant. Unless, of course, you wish to experience firsthand what it feels like to be boiled alive like a lobster in a pressure cooker. Do not use the showers, do not use the sinks, and don't you dare go near the creek. Until further notice, you will get your water from buckets brought to you by the nymphs, and I suggest you coordinate well among all your dysfunctional cabins, because the water they bring will last a maximum of ten minutes before evaporating or turning into acid."
A murmur of panic and complaints rippled through the tables, but Mr. D silenced them with a withering glare that caused grapes to sprout from the ears of a boy at the Demeter table.
"Silence. There is more," Mr. D continued. "You will be granted exceptional permission to use communication devices to call your mortal relatives and warn them to stay away from the ocean. Megalodons are running amok along the entire East Coast until further notice, and from what I gather, most haven't tasted mortal flesh in a few eons, so they are starving. If you have complaints, don't look at me; go cry to the sea gods. You are always welcome in their abyss. After all, they need more animals and cannon fodder to replenish their ranks."
Dionysus let out a dramatic sigh, preparing to turn around and return to his pinochle game with Chiron, when his purple eyes wandered across the pavilion and stopped, with pinpoint accuracy, at the Hermes table. Specifically, on the baby in the orange T-shirt, who had just finished her bottle with a loud burp.
For the first time in camp history, Mr. D took the trouble to stand up from his chair during breakfast. He walked slowly down the center aisle, causing the demigods to cower in their seats as he passed. Reaching the Hermes table, he stretched out his pudgy hand and, without the slightest delicacy, grabbed the baby by the back of her camp shirt, lifting her up by the scruff of her neck as if she were a puppy or a rabbit.
Baby Perseidas was left dangling in midair, kicking her legs weakly in her denim shorts, glaring at the wine god with the exact same scowl from a moment before.
"So, this is where you were, brat," Dionysus said, swinging her slightly in front of his face. "Your grandfather is throwing a tantrum of catastrophic proportions on Olympus. Right now, he wants to decapitate Zeus because he thinks he kidnapped you to prevent some destiny nonsense. Next time, leave a note for your mother before escaping your crib; it would save us all a massive headache."
The dining pavilion fell into a silence so absolute you could have heard a pin drop. Luke felt his stomach drop to his feet. Grandfather? Mother?
Dionysus shifted his gaze to the campers at Table Eleven, who were backing away in terror.
"Well, which one of you found her floating around or whatever?" the god asked, looking thoroughly bored.
Immediately, one of the younger Hermes kids, terrified by the divine pressure, raised a finger and pointed without hesitation toward the end of the table.
"It was Luke!" the rookie squeaked. "Luke brought her back from the woods last night!"
Dionysus turned his head toward Luke, narrowing his eyes with a mix of surprise and annoyance.
"Perfect. Lucas Castillo, you are coming with me to Olympus right now to explain to the Big Three what on earth you are doing with the daughter of Mars. With any luck, Poseidon might reward you for finding his granddaughter before the Atlantic finishes swallowing New York. Move it."
Luke stood up from the bench mechanically, his legs feeling like lead and his brain trying to process the information at the speed of light.
The daughter of Mars?
He stared at the baby dangling from Dionysus's hand. Clarisse's mention of her last night... hadn't been a coincidence. The baby wasn't Perseidas, the nineteen-year-old daughter of Poseidon he had sent for. The baby was Perseidas, the daughter of Poseidon's actual daughter and the Roman version of the god of war, Mars Ultor.
He had kidnapped Poseidon’s granddaughter and the daughter of the most violent Roman war god of all. And now he was heading straight to Olympus, into the eye of the storm, to hand the child over to a sea god who was five minutes away from unleashing an aquatic apocalypse because he thought his family was under attack.
His plan of perfect manipulation had just turned into an extreme survival mission in the throne room of the gods.