Disclaimer: I don't own The Percy Jackson books, if you recognise a character then they're not mine. If you don't then they're mine.
Author's note: I know 'Percy's younger sibling' fics are really popular, but I've tried to do something a little different. This is my first fic so I'm not used to the style or anything, if something doesn't work tell me. I'm all about contstructive critisim so please leave some.

Prologue:

Waves lapped gently against the wooden pier, the sound deepening as it travelled through the wood. A four year old girl dangled skinny legs over the side, eyes wide with wonder. Just for a moment the young woman - her mother - turned to the man beside her. For one fatal moment they were distracted; lips met and time seemed to stop, for just one innocent moment.

"Horsey!" The child's voice rang out in unison with a splash. Both adults turned towards the girl, seeing only a flick of scaled tail and then nothing. "Kal!" Her mother screamed as the man dived in after the child, finding himself unable to see through the disturbed sand. On the pier tears rolled down the mother's face. She'd had a bad feeling about this from the start and now her girl was gone. When the man surfaced she met him, her eyes without hope. He held her hand as he called the police.

An ocean apart

Kal watched the man, once a boy, brandishing a glowing bronze sword. His green eyes flashed and from behind him a boy with a black blade slipped out of the clinging darkness. Together they made short work of the two creatures before them; they had the tops of women and scales which covered clawed arms and horses legs. Behind them, horse tails flicked in anger. As they were slain, the creatures burst into dust, delivering the two, now awakened, children from danger. She felt she should know the boy; something about him was strangely familiar.

The scene changed and once again she watched him, as a boy, and a girl walk across a bridge in the sky, towards a great mountain; where once great palaces had stood but there now lay shells of buildings. Both heads were bent in discussion and every so often the girl would point at some pile of rubble or half rebuilt structure. For a moment she held bated breath, always the same dream, would it break as usual? They stepped off the bridge, the image shattered, leaving darkness.

Kal jerked awake, disturbing the water around her. One of the hippocampi stirred slightly beside her. Kal whinnied softly, calming it. Entwining her self around the thick stem of seaweed once more, she went back to sleep - for all the World as if sleeping underwater with a pod of half horse, half fish creatures was normal behaviour for a six year old.

Once again she dreamt about the same boy, only this time he was wading into the sea. In her head echoed numbers, and somehow she understood what they meant without knowing what they were. They meant positions, but she didn't know how they changed. She knew that she was supposed to travel to where these numbers were, numbers it felt she'd always known. It was imperative, she felt, that she got there quickly and safely though she couldn't understand why.

Morning light was dim in the shallow waters, but it never mattered to the creatures who lived there: life merely went on, without rush. When the hippocampi tired, they wrapped themselves round the stems of the nearest underwater forest. It was a leisurely lifestyle where very little happened at pace, it was broken mainly by playful visits to the surface. After all the hippocampi were fun loving creatures. Nevertheless, they had their share of problems: many sea creatures saw them as a tasty meal. Of course, their adopted child was more then equipped to deal with these creatures. Whenever she felt threatened, creatures came at her call. As she grew the call became stronger, though her need also became greater.

The hippocampi stirred and munched on some of the seaweed forest before setting out again. The weather was glorious, the sea glass calm, so it was only natural to surface so they could play as they swam, dancing in the shimmering sun. Above them the sky was a perfect blue and the sea danced with greens and blues. They didn't have to worry; few predators attacked them with their foundling near by. They travelled slower than usual, playing all the way. Kal was a strong swimmer for her age, boosted by the submersion in sea water, but even she wasn't able to keep pace with the hippocampi. Instead she rode on their backs as they played, ducking and diving in complex patterns. She giggled, not fearing mouthfuls of water as any mortal child would have, and called to them in the complex series of whinnies and neighs that made up their language. Over the commotion she tried to explain her need to travel, she didn't know exactly where, just that it involved the numbers she'd always known. Numbers that whispered in the back of her head, ever shifting. Numbers that she knew kept a record of her position, though in relation to what she couldn't fathom.

The hippocampi understood, they vaguely remembered tales of such a boy, with his glowing sword and green eyes. She told them straight ahead, the numbers were increasing, getting closer to the target. Though the hippocampi were coastal creatures they'd explored this sea before, travelling with the currents and the seasons. Besides the water was cleaner away from land and the feeding better, though you had to dive deeper for food and that meant more predators; the mythical sea beasts of legends lived in the deepest caves of the oceans. Beneath the rolling waves also lay the palace of the great sea god, king of all beasts in the ocean and ruler of horses, a palace little visited by the hippocampi and their relatives, creatures who were hunted rather than hunters and who lived in higher waters. The hippocampi being both horse and fish they spoke of him with reverence and a tinge of fear.

For days the weather held, they travelled mostly on the surface enjoying the sun shine as it danced with them on the waves. Then over the course of a night the weather switched, turning from perfect calm to horrendous storms, the wind calmed suddenly and slowly rose, whipping the once rolling waves in to sharp, frothy peaks. In immediate response the hippocampi stopped playing in the waves and dived, it was much quicker and safer to swim below the turbulent waters. No sea creature would dare risk the crashing mass of water and the mountainous heights. Trying to ride a storm was dangerous enough for a ship, a titian of iron, but for a pod of small, scaled animals it was suicidal. They also knew with the currents below the surface unpredictable from the waves' swell, so stopping to rest in these deep waters wasn't an option. Instead they paced themselves, most sea creatures could swim indefinitely if they needed to. Kal was unable to keep up the same pace so instead rode a larger hippocampus, he was big enough her weight barely affected him.

The storm raged for little more than a day, though below the tossing waves it remained consistently dark. Silently the pod travelled on, faster now because they didn't stop or slow. As always the mood of the weather affected the mood of the ocean below, with the anger came a fearful calm. The water itself seemed tense, as if it was waiting to see how powerful the storm was going to be, waiting to see how far it would delve in it's fury. The shadows cast by unbroken clouds meant even meters under the crashing waves there was little light. In the middle of the sea light mattered little, there weren't many obstacles in the way, nothing to crash into.

The only need was food, this far out there was no plant life to be munched up. Instead the hippocampi fed upon the tiny creatures that floated through the water, keeping their mouths open to gather as much as possible. Kal fed upon the fish that swam the waters, catching and eating the fish raw. This had been a problem at first, but hunger quickly over took any repulsion at the process. Her instincts told her which fish were good to eat and the creatures were too intrigued by her to dart away. She quickly became used to the taste and the process, slicing them open with a sharp piece of shell one on the hippocampi had found for her. In time they'd been travelling she'd become proficient enough to gut them while riding; this allowed the pod to keep moving and allowed them to eat up the distance.

The journey was swift and uninterrupted. Mostly the sea creatures left them alone, except for shoals of edible fish which swam around these travellers with interest. On the surface the hippocampi could travel faster than a jet ski in small bursts so they made good time, despite the slower pace. In less than a week the coast was in sight and the water shallow and warm. The pod ate their full, something they had not done while on the journey. They took rest at the first underwater forest they sighted, grazing contentedly before wrapping their tail, or legs, around the tough stems and sleeping.

Kal was awoken by something nudging her sleeping form, she opened on eye and was met with the sight of a white form that filled her view, and behind her she could here the scared whinnies of the hippocampi. The white form raised its head to her and slowly opened its mouth. She froze in terror; it was huge, could have swallowed her whole and had rows of bloody, pointed teeth. In a second she knew if she moved it would eat her alive, but she feared if she didn't it would take a bite out of her too. She caught its eye and held her breath, nothing happened. It nudged her again and she froze. She waited another moment and carefully reached out a hand to pat it. The creature nudged her hand slightly. She realized it wasn't going to hurt her, it was being friendly. She called out to her pod, telling them in a series of neighs that it was okay; her new friend wasn't going to hurt them. She figured it was here to protect her.

They set off again, this time limited to the speed of the shark. On the other side of the ocean the fish seemed bigger and there were more. With the shark at their side none of the other creatures dared to come near them, though they watched from the shadows with interest. As they drew closer to the destination she started to pay more attention to the numbers in her head.

The water became more and more polluted, limiting sight. In response the pod swam on the surface. In sigh of the coast they caused a wave of shock and confusion to those who saw them. No mortal could fathom why a child was riding a dolphin escorted by an entire pod and great white shark. None of the travellers noticed the attention and so the confusion grew, with more important people being informed all the time.

On land a camera crew had gathered and was following their progress. Everyone, from the amateurs to the highest marine biologists, was trying to explain this strange phenomenon. The media was relaying their progress ahead, it didn't take long before it was realized they were heading down the coast towards New York.

Every watch station along the coast was put on alert, on all the beaches people were warned and lifeguards went on stand-by. In New York itself a warning went out, no one was to approach the travellers. Leading experts on aquatic life jumped on plains, in cars and headed for the city. They hoped to intercept the group and hopefully engage the human child in conversation.

It was the buzz of a helicopter over head that alerted the pod to the fact they were being watched. Automatically they dived, partially because they didn't like the noise and partially because Kal felt it was bad, like they shouldn't be. They were still in deep enough water to disappear completely below the waves and this baffled the mortals again; dolphins were not known to hold their breath underwater for longer than 8 minutes and these never surfaced again. The fact a human child could do the same lead to the conclusion she probably had a breathing apparatus, though this made no sense to the ordinary people who had seen her.

Travelling faster than they had been above the water, they reached Long Island just before the evening, as the sky was beginning to glow slightly pink. They stayed deep as they could before approaching shore. The water quickly became too shallow for the shark and Kal had to say good bye, though it circled the water near by waiting to see if she would return. As a pod they approached, remaining underwater for as long as possible before being forced up and out of water. The first thing she saw was a beach, the surf breaking gently on the shore. Slightly above that sat two people, curled up together on a blanket. She didn't have to be any closer to recognise them as people from her dreams, the boy with green eyes and glowing sword and the girl he'd spoken with.

Keeping her voice as quite as possible she whinnied to tell the others to be quiet, it felt right to surprise them and she didn't trust land walkers, they poisoned the water and threw things at her. A couple of the hippocampi told her she was being silly, that she should turn around and walk away from them; they were land walkers and ultimately trouble. She replied that she didn't have a choice, they'd come this far and away it felt right to be here. Slowly they moved through the water, once she could feel the sand beneath her bare feet she signalled to let the other's know she wanted to go on alone.

Then she was there, exactly where he had been, but it wasn't important now. She knew she had to go to them, they were important. It was why she had seen them in her night visions. But Kal was scared, a girl who had faced a shark, befriended strange creatures and travelled an ocean was afraid. The sea was safe, she knew it;' she had friends. She was trading all this in for a taste of the unknown, an urge, an impulse.

Silently she approached the shore, keeping as low as possible to keep from disturbing the surface of the water. Slowly the water above her became shallower, until she was dragging herself out. With each movement it felt like more weight was being added to her body. She lifted herself off her tummy with great effort before starting to crawl. She was almost out of the water when her eyes, fixed on the couple, saw movement and she froze.

The boy had glanced in her direction and though she froze, crouched low in the shadows he saw her. She heard him talking to the girl, though it was the jumbled mess of a forgotten language, before they stood up and approached her slowly. Something crept back into her mind, land people walked on two legs, not four like she was doing. With a frown she shifted her weight to her legs, but everything was so heavy now; she could have been made of rock. Even just that movement left her too tired to do any more than crouch. Neither of the couple had taken their eyes off her, though they moved steadily closer treating her as they would a wild animal.

Percy couldn't believe his eyes, there emerging out of the waves was a child, a little girl. Her dark hair was matted, left loose and raggedly long, and her well worn, torn clothes were far too small. The only other details he could make out were a strong face, wide, green eyes and the fact she was completely dry. Those eyes watched him with an intense wariness he'd only seen before in wild animals. Gently he nudged Annabeth, whispering to her to keep quiet. "Who is she?" Was the daughter of Athena's initial response.

"How should I know, I thought you knew everything." Percy retorted.

Annabeth rolled her eyes before easing herself to her feet. "Come on, let's find out seaweed brain."

Finally, the pair stopped at a respectful distance from the child. Percy crouched down to her height and kept eye contact as he raised a hand in greeting and said ever so gently "Hello." Kal watch with wide eyes, looking for a moment as if she were about to pounce or scuttle back to the sea she'd come from. Instead she kept staring at him, unblinking, as she raised a hand in imitation and said in a funny half New York, half English accent.

"Hello."

Percy was the first to break eye contact, glancing at Annabeth with a raised eye brow. "I'm Percy and she is Annabeth." He waited a moment, trying to watch the child's face. It remained almost completely motionless, though a very small frown appeared as if she were concentrating. "We won't hurt you. We are friends." Her expression didn't change, but she didn't dive back into the water so he figured they must be making some progress. "Who are you?" The girl's frown deepened, she opened her mouth slightly but said nothing.

"Percy, Annabeth. I friend. I" The words were long and over pronounced as if she were still making sense of them, and she finished her sentence with a snorting whinny.

Shock and confusion flickered across their faces, and the two turned to each other seeing their own questions reflected in the others' eyes. "Annabeth, you go get Grover I'll try and get her to come to camp." Annabeth almost objected, but decided against it. Instead she stood up and backed slowly away from the girl before running towards the spot where she knew Grover would be. Kal's eyes didn't follow her, but remained firmly fixed on Percy's.

"I help you. You come with me. Have food. Be safe." Percy made sure to keep his voice level, to speak slowly and clearly, silently willing her to understand and to agree. There was a long pause and her frown lifted slightly.
"Yes." was all she said and then she tried to stand but only managed to wobble for a few moments before the weight forced her back to the ground. Percy watched all this, wondering what to do as she clearly couldn't walk very far. He doubted it would be a good idea for her to crawl back to camp but the only other solution was for him to carry her. He inhaled slowly and looked at her calmly, questioningly, making sure to put in the right inflections. "Carry?" A beat and then her eyes lit up.

"Yes. Carry."

Percy was almost surprised, but then he remembered his younger half siblings, now nearly eight and five, they always demanded 'carry' from him or his parents when they became tired. Carefully he moved forward, keeping her eye contact, until her could lift her up into his arms. Kal was still to wary to relax, but she felt to heavy to object, instead she tensed slightly just in case something went wrong. Percy in contrast was surprised she was so light; he supposed she was little more than skin and bone. Moving slowly so as not to startle her he carried the child towards camp, hoping Grover would be here soon to provide much needed translation.