Author's Notes: I've actually only read the first Percy Jackson book so far, but I've spoiled a lot of things for myself on the Riordan Wiki. Apparently Unnamed Nereid never shows up again or gets expanded on? I expected her to be a recurring messenger from Poseidon or something. Anyway, this is for the Writer's Month prompt "Water," though I started it last year for the prompt "Ocean." Enjoy!

It was a beautiful day at the beach, but Sally Jackson was having a hard time enjoying it. She was too busy trying to keep her three-year-old son away from the water.

"No, Percy! Come here."

He squirmed in her arms as she carried him back to their blanket. He began to whine, so she reached into the cooler and fetched him a juice box. He stared longingly at the ocean as he drank.

Sally sighed. Bringing him here really was starting to seem like a mistake.

Sally loved the beach. Especially this beach, where she had met Percy's father. This was the first time that she had been back since he went home. She had been afraid that it would be sad place for her now. Or maybe even a dangerous one.

And it could be even more dangerous for Percy. Poseidon wasn't the only sea god, and his relations with the others weren't always friendly. Not to mention all of the different monsters that could be dwelling under the surface.

Sally had already learned that trouble was drawn to Percy like a magnet. And unfortunately, he seemed just as drawn to that big, beautiful expanse of water that waited ominously across the sand. Sally watched its waves break on the shore, imagining them as hands reaching out to snatch her son away.

"Let's play in the sand," she suggested, forcing a note of cheer into her voice.

"No! Wadder!"

"Not right now, Percy. Come on..."

He kept whining, but Sally got out the plastic shovels and buckets. Her attempts at a sandcastle proved both sloppy and, to Percy at least, insufficiently entertaining. Burying him in the sand proved more successful; after a few minutes Percy became absorbed in the job of digging what seemed to him as an enormous hole, and he giggled as Sally pushed all the sand back in, burying him up to his neck.

"Okay, Percy, how's that feel?"

"I'm stuck!"

"You're stuck?"

"Stuck!" Percy agreed, giggling and spitting sand out of his mouth.

"Oh, you can get out if you really try. Can you be really strong?"

Percy made an exaggerated groan of effort. He wriggled his shoulders until the sand around him started to crack, then managed to burst out of the ground, waving his hands and laughing as Sally praised and applauded him.

Unfortunately, there was a problem she hadn't thought about: Percy was completely covered in sand from the chin down. "Wait here," she said after a moment of thought, taking the bucket to the shoreline. Her body tensed a bit as she bent down and claimed a bucketful of water; she half expected a sea monster to burst out of the surface and swallow her whole.

Percy laughed some more as Sally dumped one, two and then three buckets of salt water all over him, with the last dumped right onto his mostly-clean head. He got fidgety again as she wrapped him in a towel to dry of.

"Can I play in the wadder now?"

"No, Percy. It's too dangerous."

"But I wanna!"

Sally thought quickly for another distraction. "Why don't you dig another hole? Sometimes you can find water if you dig really deep."

"I can play the wadder?"

"Not—not that water," she said desperately, turning his gaze away from the ocean. "Come on, I'll help you get started."

She started to dig another hole with him. Once again he got caught up in the task, and after a minute Sally scooted a few feet away, content to watch him work with childish diligence. She smiled wanly as he accidentally knocked a pile of sand back into the hole, then grunted with every shovelful that he threw over his shoulder.

My little boy, she thought. A breeze blew by, ruffling his hair, and she was struck once again by how much he resembled his father. An adorable little replica of him, finally here on the same beach where the two of them had first met.

Now that she had a moment of rest, Sally was finally able to feel all of the emotions that she had expected and worried about with this outing. Happiness and sadness, mixed into a wistful nostalgia. Good memories and the dull ache of loss. Poseidon was the only man she had ever really loved, even as she knew, now more than ever, that everything about them had been impossible from the start. But still, here was Percy, his very existence in defiance of that fact.

As she allowed her mind to wander, Sally also let her gaze drift away from her son for maybe thirty seconds. Of course, anyone familiar with toddlers knows that that is a rookie mistake, and when her eyes turned back toward the hole, Percy was obviously gone.

"Percy?" She looked around, then jumped to her feet. "PERCY?!"

She quickly looked to the water and nearly fainted.

A seven-foot wave was headed toward the shore; it towered over every other breaker that they had had that day, unnaturally tall given the placid weather. And there, sitting on top of it, was Percy. Not submerged, not struggling to keep his head above water, but sitting, as if he were being carried by an unseen surfboard. He leaned back with his little feet in the air, waving his arms and squealing with excitement.

Only when the wave broke did Percy finally disappear into the water. Sally gave a soft scream, but as soon as it withdrew he was standing right there on the shoreline, clapping his hands and laughing. He turned to run back into the ocean, but the water was only up to his knees before Sally rushed over and managed to grab him.

"No! No, Percy!"

He whined again, struggling in his mother's arms. Sally quickly walked ashore, looking around. It was a weekday, and this spot was fairly secluded; an older woman slept on a folding chair about twenty yards away, but otherwise the beach was empty.

"Wadder! Wadder!" Percy whined. "I wanna play with her!"

Sally froze as she deposited him back on their towel.

"Play with who, Percy?" She forced herself to stay calm, but took his face in her hands, looking him straight in the eye as she spoke.

"The girl in the wadder," Percy said, pointing back toward the sea. "Can I play with her?"

Sally hesitated for several seconds, then brought out the big guns.

"Let's go get ice cream!"

Needless to say, "the girl in the water" was quickly forgotten, at least by Percy; Sally thought about her for the whole trip to the boardwalk and back. A siren? Those lured people into drowning, but they didn't go into the water themselves, did they? And besides, Percy hadn't drowned...if anything, "the girl" might have saved him. So she was something benevolent. At least, in theory.

Sally wouldn't give Percy his ice cream until they were back on the beach. He immediately asked to go in the water again, but she explained that he couldn't until he was done eating.

Then she buried him up to his waist in the half-finished hole. He laughed, twisting his body as he smeared his face with ice cream. Hopefully this would keep him from running off for a minute or two.

"Now you stay here. Mommy will be right back."

She stepped cautiously toward the water. Stopped when the breakers hit her ankles. Glanced back at Percy, still eating his ice cream.

"Alright, who's there?"

She wasn't sure if she would get a response, but she scanned the water, and suddenly there was a face where there hadn't been a second before. It looked like a reflection, right about where Sally's own should have been, except that this woman had long, black hair and a pale, delicate face that was inhumanly pretty.

Sally's breath caught in her throat.

"Greetings, Sally Jackson." Her voice was soft, but somehow audible over the sounds of wind and waves.

Suddenly the water rose up, as tall as it had been when it carried Percy. Sally jumped back as the wave hit the shore; when it cleared, the woman was standing there, calm and perfectly dry. Her hair and dress flowed in the breeze; her skin seemed to glow green, which flashed like sunlight reflecting off of the surface of the water.

Sally glanced back at Percy. He had freed his legs from the hole, but seemed content to stomp in the sand, looking in the opposite direction. The older woman in the beach chair was still napping. Sally turned back to the newcomer.

"Who are you?"

"I am a Nereid. A nymph of the sea," she added, as though it had just occurred to her that Sally might need an explanation.

She didn't. Her limbs stiffened and she took a cautious step back, but tried to keep her voice calm.

"May I ask your name?"

The Nereid turned her head slightly.

"I am Sao," she said. Then, "Were you expecting perhaps my eldest sister, Amphitrite?"

Sally nodded curtly.

"Do not fear. She knows about your son, but bears him no ill will." She paused, a slight frown coming to her otherwise impassive face. "You...are probably safe, as long as you don't see Lord Poseidon anymore. But if you ever meet my sister, I suggest telling her that you didn't know he was married, whatever the truth may be."

Sally made a "hmm" sound in the back of her throat. "So who sent those snakes, then?"

"Pardon?"

"The snakes that attacked Percy in daycare."

Sao put her finger to her chin. "Hera, perhaps."

"Would she want to kill Poseidon's son?"

"Not particularly, but if she sensed a powerful demigod she might have made assumptions."

"Percy isn't 'powerful.' He's a little boy." Sally glanced back at him, suddenly paranoid that she would find him fighting off more snakes or something. She turned back to Sao, speaking cautiously. "If you don't mind me asking...what are you doing here?"

The Nereid smiled wanly.

"This is the first time that you've brought your son to the border of his father's realm. Everyone in the court has been hoping to see him."

Sally suddenly realized that Sao was gazing past her, watching as Percy took handfuls of sand and threw them up in the air. Sally winced, and without thinking called, "Percy, stop! You'll get sand in your hair!"

If Percy heard her, he didn't listen. Sally sighed wearily.

"Toddlers."

"Yes, I remember when mine were that age," Sao said wistfully. She continued, "You are wrong, however. Poseidon's son radiates power, even now. He will be a great hero if he survives long enough."

Sally stiffened again.

"In any case, you need not fear the sea, Sally Jackson. Any beach that mortals frequent should be safe. At least for now, Lord Poseidon's realm is at peace. And as his child, young Percy draws strength from the water."

"Well, he does love bath time."

"Hey, Mom!" Percy called suddenly. Sally turned; he was holding up something white and shining. "What's dis, Mom?"

"It's a shell, honey."

"Can I have it?"

"Sure."

He toddled over, turning it over in his hands. Then he asked, "Can I play in the wadder, please?"

Sally turned. She suddenly realized that Sao had vanished. It was as if she had melted back into the ocean.

Sally hesitated for a moment, then smiled down at Percy.

"Alright. Let's put your shell away, then I'll teach you how to swim."

"Okay!"

Mother and son walked back to their blanket, hand in hand.

Sao, now visible only as a reflection on the water, gave a small smile before disappearing completely.