Katie set her black leather camera case down gently by the back door. It was well padded to protect the device inside, but she still had no intention of risking damage by dropping it or tossing it around. It was currently plopped beside the well-worn olive-toned backpack she carried everywhere.

Lifting her wrist, she examined the light turquoise, heavy-duty plastic of her dive watch. She had about an hour before she had to be down at the docks. It was a fifteen-minute walk, so she had some time left before she had to leave. Pivoting on her ankle, she walked back down the hall to her room and crouched down in front of her dresser. She tugged open the bottom drawer and began rifling through the many pairs of shorts that were neatly folded within. She wanted a spare change of clothes just in case.

Consumed by her task, Katie jumped and barely bit back a startled shriek as a wet, slender hand wrapped around her ankle. Spinning around, she lost her balance and plopped down on her rear as she stared at her playful assailant. She crossed her arms and frowned at the younger girl peering up at her.

Luna had her tongue poking out between her teeth and her lips were pulled into a wide smile. Vivid, crystal blue eyes shone with mischievous delight, broken only by a hilarious expression as she attempted to blow some of her wet bangs out of her eyes. Like the rest of her hair, they were long and sodden with water, the soft brown tendrils clinging to her skin. She sighed and raised her other hand to shove the cascade of hair back off her face. “Got you,” she taunted with a giggle.

Katie’s frown deepened and she bit back a chuckle at the pre-teen’s antics. “That wasn’t very nice,” she scolded. “Just because you can pop up out of nowhere, doesn’t mean you should; and you certainly shouldn’t do it to scare me out of my wits.”

Despite her chiding, Luna’s grin only widened. It was infectious, and Katie lost the battle with her own expression as a wide smile flowed across her features. “I know,” Luna lamented, though her joyful expression did not falter. “But your expression was worth it; I could not resist.”

Katie forced a scowl onto her features and dipped a bare foot into the tiled basin Luna was resting in. She flicked water at her younger sister, but Luna merely blinked and giggled, completely unphased by the onslaught.

Luna crossed her forearms on the edge of the actual floor of the room and rested her chin on them. Her smile turned sly and she raised her sky blue fin into the air, slapping it back down on the surface of the water so that droplets lurched up and rained down on Katie.

Katie gasped and scrambled away as a dark patch began spreading across her lime tank top. “Luna!” she exclaimed. “You’re going to soak the bed, you better hope you didn’t get any of my pictures wet.”

Luna's tongue was between her teeth again - the canines lengthened into long fangs - and she shrugged. “It is only water,” she countered as she pulled herself up out of the pool. Rippling sapphire scales shimmered with dancing flecks of purple and green in the light streaming from Katie’s open window as Luna settled herself on the floor and pulled her tail close. Katie snatched a folded towel from the top of her dresser and flung it at the young Mer.

“You’re such a pest,” Katie complained as she opened another drawer and tugged out a new shirt. She ripped her soaked one off and pulled the fresh tee over her head. What had initially been extraordinary had become mundane for her over the years. Mermaids - or Mer as they preferred - existed, and she lived with one. Katie was adopted, had come to live with her godmother - Sophie Brooks - when she was eight years old. After her father’s death, her flakey, workaholic mother had dumped her on Sophie’s doorstep and taken off for America. Roxanne had never wanted kids, and while Katie had initially struggled with abandonment when she was young; she was more than content with the life she led now.

Like her, Luna was also adopted. Sophie was the owner of a very successful marine park about half an hour up the coast. They ran a rescue and rehabilitation program out the back, and it was initially how Luna had come to be in her care. The young Mer had been tossed from the sea in a particularly brutal storm as a toddler. Sophie and her team had found her while combing the beaches for strandings. She had been scraped up pretty good, with several deep lacerations and a broken arm.

Though Katie had not been present, she could only imagine her adoptive mother’s surprise at the discovery. But Sophie was a professional, and they’d taken Luna back to the park for proper medical treatment. Katie wasn’t yet living with her, so the entire early story was second hand, but she knew that Luna had not been the easiest patient. She was squirmier than a regular human toddler, with tiny pointed fangs and a slippery tail with sharp scales that could easily split skin if not handled carefully. She had been chittering in a dolphinesque language that no one could understand, and was believed to be little more than an intelligent animal.

Over time, as they treated her, they began to discover just how intelligent she really was. Sophie had kept Luna quiet at first, believing that the discovery would have a negative impact on the frightened baby and impede her recovery process if a bunch of eager faces were pressing in on her at all times. Instead, they’d kept her in a back pool with the intention of eventually rehoming her properly in the park. Sophie had looked for any sign of a pod or parents out in the water, but had been unsuccessful, and without them, Luna didn’t stand a chance at survival.

Sophie had given Luna her name, inspired by the butterfly-esque eyespots on her fin. Two dark, navy circles with a brilliant white ‘eye’ in their center. Her mother had spent quite a bit of time socializing Luna, using her name and talking to her to attempt to adjust her to human interaction. Luna healed well, if a bit slowly, but Sophie had been reluctant to announce her existence to the world until she had truly settled down.

After about a year, Luna finally uttered her first English word - ring - while reaching towards the box that held her toys. To this day, Luna loved the old, orange rubber ring from her childhood. When Sophie became aware of her sentience, her plans for Luna’s future changed drastically. Katie had only just come to live with her by then, and Sophie had dipped into the large pool of funds she never felt the need to touch before.

She’d had the incredible two story beach house built on a private little cove, and had outfitted the walls and floors with an intricate series of tunnels and waterways, some that were visible through glass windows, overs covered with drywall, and all opened into special pressurized pocket pools like the one in Katie’s room to give Luna a place to swim and an easy means of getting through the house.

Only a few select individuals knew of Luna’s existence and they were very careful. They rarely had company over and Luna was not allowed out front or near any front facing windows unless she carefully concealed all her inhuman features. Katie didn’t mind the restrictions though. She and Luna had bonded closely - Luna only tended to be this cheeky when they were alone, having a much quieter and shyer demeanor with Sophie and Lewis - the sea vet who had rehabilitated her and was like a fatherly uncle figure to Katie now that he and Sophie were in an intimate relationship and he was living with them - she still talked and laughed and played, but it was never quite as boisterous as when they were alone.

“Where are you going?” Luna inquired as Katie fished out the change of clothes that she had wanted.

“For a dive,” Katie replied.

“May I come?” Luna asked eagerly, leaning forward slightly on her palms as she spoke.

Katie shook her head. “Not this time, Lu. Sorry, you know I love diving with you, but this isn’t a solo dive. I’ve been hired to take pictures for a wedding excursion.”

“Oh.” Luna’s shoulders slumped and her gaze instantly turned downwards as she traced a finger over the wood floor of the room. “Have fun, I guess.”

Guilt and sympathy dug their nails deep into Katie’s gut. She knew Luna struggled sometimes with needing to remain hidden from the world. Sophie and Katie and Lewis could come and go as they pleased, but they were her whole world and they knew it. Luna hated having to hide and feeling excluded from the world beyond the house.

Chewing her lip, Katie knelt down and nudged her little sister as an idea struck her. “Hey, I have to go, but what if I stop at the store on my way home? I can pick up some of that mango ice cream you love, and then you and I can take a twilight swim out in the cove,” she suggested. “There’s a staff meeting at the park tonight, so mom and Lewis won’t be home until late. It’s just you and me.”

“Okay,” Luna agreed. She still seemed a little disappointed, but the suggestion had brought a glimmer back to her eyes and a smaller smile to her lips. “How long will you be gone?”

“Just a couple of hours,” Katie replied. “We’re going out to the reef. The couple just got married yesterday and wanted to make this whole big showcase of an underwater adventure to start their honeymoon.”

Luna cocked her head and shrugged, and it made Katie laugh. No matter how many different ways they tried to explain to her, Luna had never fully grasped the concepts of many customs and events of human beings. Katie was pretty sure the concept of a birthday confused her and that she only played along because she liked the cake and attention. Sophie had selected the day she found Luna to be the young Mer’s birthday - they weren’t even completely certain of her age, assuming her to be eleven or twelve - because she hadn’t understood the same concepts of time, and by the time they had gotten her speaking fluently enough to answer questions; Luna had forgotten quite a bit, including whatever her real name and age had been. They made substitutes for her as best they could.

A wedding and a honeymoon were both concepts that were outside her scope of understanding, so Katie just waved it off. “Don’t worry about it. I’ll be back soon enough, okay? Will you be alright here?”

Luna nodded. “I will probably just nap,” she decided. “And I can make myself a snack if I need to. I will be alright.”

“Good.” Katie ruffled Luna’s hair as she stood, chuckling at the Mer’s quiet huff of protest as she ducked away. “And stay out of the cookies,” she warned sternly. Luna had a bad habit of eating too many and making herself sick if she wasn’t supervised. Sophie would kill them both if she came home to find the unopened sleeve empty and a Mer with a bellyache.

Luna sighed and rolled her eyes. “Fine,” she muttered. “Be safe on your trip,” she called as Katie turned to leave the room.

Katie paused in the doorway to grin back at her little sister. Luna’s wide eyes glistened and her fingers were twitching into fists at her sides. Luna hated being alone for too long and Katie knew she worried more than necessary. “Don’t worry, Luna,” she assured. “I’ll be fine.”

Despite the promise, Luna’s eyes stayed wide as if begging her not to go.

Katie wished she’d heeded that.