A/N: For those of you who don't know, Nøkken are shapeshifters from Scandinavian folklore known for appearing (most often) as handsome young men who hang around water and play the violin to lure women and children to their deaths by drowning (comparable to the Greek Sirens, the Slavic Rusalka, and various other water nymphs from world mythology). Nøkken are not always malevolent, however. There are accounts suggesting that they were most active on Thursdays or during the change from spring to summer and from autumn to winter.

Special thanks to rottenbrainstuff on Tumblr for the idea of Nøkklock.

Molly Hooper had hated Thursdays ever since she was a little girl. Her father had died on a Thursday and she had never been able to shake the uncomfortable feeling that left. Thursdays also meant a long day of work, hurrying about the village with whatever tasks her guardian, Mike Stamford, gave her. She never came away from a Thursday feeling anything less than exhausted.

Molly Hooper's feelings about Thursdays changed not long after her nineteenth birthday. It was nearing Midsummer's Day and the village gossips had just taken a particular liking to talking about her. They called her strange. One woman had gone so far as to suggest that she was a changeling, which prompted more than a couple of parents to keep their children away from Molly. These conversations which the young woman had overheard all eventually led to the same topic: how none of the men in the village would marry her. Molly was of the opinion that any man who could not love her just as she was was a man not worth wedding. Mr. Stamford told her that she needed to have more practical considerations. As much as she loved and respected her guardian, Molly couldn't bring herself to consider his words.

Molly was something of an idealistic dreamer and as such, she spent many an evening just sitting and taking in the world around her. One particular evening, when Mr. Stamford was out discussing preparations for the upcoming festival and she was inside, gazing out her window, the faint sound of music reached her ears. It was a violin being played and oh what sweet song it made. There was a sadness to the tune as well and its distant sound created a slightly haunting effect. It captivated Molly and she listened to it for hours into the night until the music faded.

This occurred many Thursdays hence and each time, Molly's curiosity about the source of the music grew. Who was it who made such beautiful song which she had come to look forward to?

One night, Molly made up her mind about it and sneaked out of the house, quietly following the sound of the music. It led away from the village and into the nearby forest. This strangely did not concern her. She was focused solely on finding the one who played the violin so masterfully. She came upon a stream where the music seemed to be at its loudest and clearest. Looking about, she spied a very handsome young man perched on a boulder in the stream, playing away at a violin.

"You play beautifully, sir," Molly called, grinning, but the young man ignored her until he had finished the tune.

"I've been playing for weeks at yet it seems that only you have heard my song," the young man finally said with a hint of irritation, lowering his lovely instrument. Molly could see now that there was a water lily tucked in the lapel of his elegant black coat. He was frowning slightly at her with his thick eyebrows, which were a somewhat gingery shade in comparison to the inky black curls atop his head.

"I live in the outermost edge of the village, sir," Molly replied sweetly. Of course only she would come if only she had heard the song. He quirked an eyebrow at her and hopped gracefully from the rock to the bank of the stream.

"You are not like the other villagers," he commented, narrowing his eyes at her. What he had seen in her to make this statement, she did not know.

"I'm just Molly."

"Nobody is just anything. I've heard your name whispered, heard the other humans talking about how different you are." The young man came much closer to her as he spoke and the rich baritone of his voice sent shivers down her spine.

"Well, that's one way of putting it," Molly responded shyly.

"Yes. They use harsh words, cruel even, when they speak of you, but all it boils down to is a hatred for those who are different. That quality is not an evil in itself, Molly Hooper. You need not feel any shame for it." If she was charmed before, she was completely enchanted by him now. She didn't even think to stop to consider that he was a stranger who somehow knew about her and who possessed a rather magnificent pair of pointed ears.

"You're very kind, sir." The young man was thoroughly taken aback by this, as if her words were somehow revolutionary. After seemingly recovering from his shock, he stepped even closer to Molly, making the distance between them rather intimate, so that he could whisper in her ear.

"If you mean that truly, find this spot again tomorrow night without my music to guide you." Molly let out a small gasp at this and before she could think to say anything properly, the young man had jumped into the stream and disappeared.

Molly remembered his instructions and she was eager to make her excuses to Mr. Stamford the next evening after the day's work was done. Once she had satisfied his questions, she made her way out to the forest, doing her best to recall the path she had taken the night before. Her heart was filled with the desire to see that unusual young man again. He was beautiful and wise and made her feel things that she had never felt before. Unfortunately, finding the place where she had met him previously was not as easy as she had imagined it would be. There was a certain amount of sameness in the forest that made finding one's way something of a challenge.

Molly had been wandering about for just over an hour when she heard it: the sound of running water. Her heart soared as she started to run towards the noise. Soon, the faint scent of water lilies filled her nose and she remembered the water lily that had been tucked in the young man's lapel. Flowers didn't grow in running water, so it could only mean that she was getting closer to her destination. She broke through the trees to the bank of the stream and found the young man perched once again on the boulder that rose from the water, his back to her.

"I'm here," she announced and her turned to face her. For the first time, she truly noticed that he was not human. She saw his pointed ears and the blue glow of his eyes.

"Now you can see me for what I am, Molly Hooper. Do you still want to be here?" he said. Molly thought she heard a hint of sadness and resignation in his voice and it broke her heart. What kind of life must he have led to so keenly feel the sting of a potential rejection?

"I only find you even more interesting than before," she told him. For a second time, she saw him take on a look of bewilderment, but this time it was soon followed by a smile that revealed the sharpness of his upper canine teeth.

"Do you know what I am?"

"No."

"I'm a Nøkk, a water spirit from the north. Many of my kind are malicious men, but I am one of the few who have chosen a different path. All I want from you is your companionship," the young man explained before hopping once more to the bank. Molly beamed at him, her cheeks flushing with colour.

"Then you have it."

The more time Molly Hooper spent out in the forest with the Nøkk, the more she fell in love with him. Of course she would. A woman like her could never fall for an ordinary man, could she? She learnt in their time together that he wasn't just beautiful and wise; he was witty and knowledgeable. He also had a prideful nature that sometimes put him on the wrong foot with her, but in the end, she would always love him dearly.

Molly didn't know the Nøkk's name. When she'd asked, he had told her that it was safer if she didn't know. If she spoke his name aloud in his presence, he would die. She decided that she would call him Sherlock in reference to his lovely hair and he gladly accepted the nickname.

Rumors about her in the village began to run wild the more time she spent in the forest. People were saying that she laid with woodland spirits and beasts. Their opinions didn't really matter to her anymore. She only cared that she had a friend. However, Mr. Stamford became increasingly concerned by her activities and attitude. It was having an effect on his ability to provide for them both. Seeing that it was unfair for her to impose on Mr. Stamford anymore, especially now that she was a grown woman, Molly gathered her possessions in a satchel and left one night. She had nowhere to go, but she couldn't stay.

Molly's feet carried her along the familiar path through the woods to Sherlock's territory. Before she reached the brook, she came upon a small cabin that had definitely not been there any of the other times she had come this way.

"How...?" she muttered as she came up to the door, which had runes carved in it.

"I know some Huldrer who owe me favors. I asked them to help me put this together as soon as I heard of your predicament." Sherlock's voice announced his presence behind her and she gasped, spinning around to look at him, a smile of delight on her thin lips. She remembered him once telling her that Huldrer were female forest spirits who were kind to those who respected them and possessed some of the same enchanting abilities as his own kind.

"How did you know?"

"Birds are insufferable gossips, Molly," he told her with a smirk.

"You did this for me?"

"Obviously. Now go inside and assess whether it meets all of your needs." Unable to stop herself from grinning ear to ear, Molly did as he asked.

It was a cozy little arrangement with a small hearth, a table and chairs, and a bed off in the corner that was twice the size of the one she'd had at Mr. Stamford's place.

"It's lovely, Sherlock. I don't know how I could thank you enough."

"You could marry me," the Nøkk suggested casually, leaving Molly stunned. She turned to see him holding out a water lily to her, offering it up like an engagement ring. Never in a thousand years would she have been able to see this coming. Yes, they were friends, but she had always taken his slight air of detachment as a sign that he wasn't interested in her in any other way. Apparently she had been quite wrong about that.

"Of course I will," she answered, taking the flower and tucking it into her hair. Its stem extended, braiding itself with one of her brown locks.

"You are remarkable, Molly Hooper," he murmured, stepping much closer to her so that he could slowly lean down and press his lips to hers. His skin was cool, like he'd just come in from outside on a winter day, but Molly didn't mind. She was rather focused on the fact that a man she was deeply in love with was kissing her as sweetly as she had always imagined.

"I love you," she whispered when he pulled back and a softness came over his features that she had never seen before. He brushed a wayward lock of her hair behind her ear and caressed her cheek with his thumb, looking as if he were about to say something in return.

Suddenly, he stepped back, pressing his fingers to his temples as is eyes screwed shut in an expression of pain. Before Molly could ask what was wrong, he dashed from the cabin and out toward the brook. When she finally caught up with him, he was up to his hips in the water, crying out at the top of his lungs. The sound echoed throughout the area and Molly knew then that there was magic at work. When his pain seemed to have faded enough for him to stop screaming, he fell backwards into the water. Only the front of his face and shoulders reappeared above the surface a second later.

"Sherlock?" Molly called out, getting to her knees at the very edge of the stream. "What was that? What's happened?"

"A human child is going to drown," the Nøkk replied, sounding exhausted. "I saw him in my mind's eye. The path I took as a water spirit compels me to give warning."

"Are you alright? Is there anything we can do?"

"I'll be fine in a moment. What concerns me is the fact that this might mean that another Nøkk, a nasty one, has moved into my territory and I will not be allowing him to drown children in my waters," Sherlock began. His face was going very pale, but Molly knew this to mean he was recovering, so it did not concern her. "Run to the village. Tell the people that they should keep their children indoors until further notice. There is a dangerous creature somewhere in the woods."

"Right. I'll be back soon." Molly turned to leave, but a wet hand shot out from the water to close around her wrist so that Sherlock could rise up a little to give her a brief, clammy kiss.

"Be careful," his voice rumbled in her ear before he let go and sank back into the stream.

"I know." Not wasting another moment, Molly sprinted off toward the village.

The people were not happy to see her, but they listened, strangely trusting her knowledge of the spirits that resided in the forest. They had heard Sherlock's cry and were wise enough to recognize what it meant and take action. Each family scrambled to account for their children. All were collected but one: Carl Powers, the mayor's son. The boy was well known as a strong swimmer, but Molly knew that would not save him from a foul Nøkk's song.

Molly was soon off again through the forest, calling out for Carl. She heard no answer again and again and each time, her anxiety grew. Then a very particular sound reached her ears, the sound of a violin being played. The tune was not Sherlock's. This one was sweeter, more deceptive, and she wondered why she was not affected by it as she was by Sherlock's song. Then she felt the water lily her hair and theorized that it was for protection as much as it was for beauty and symbolism.

Molly followed the music as quickly as her feet would carry her. When she came upon a broader part of the stream, she knew in her heart that she was too late. Carl's shoes sat alone on the bank and a grinning man stood up to his waist in the water, looking quite pleased with himself.

"Hello there, young lady. Ah, I see another man has claimed the right to drown you. What a shame. Two in one day would have been lovely," he said as he looked over at her. He dropped his violin into the water and waded up onto land. There were water lily petals decorating his cuffs, Molly observed. He sniffed the air and continued to grin. "Oh, I know that smell. An old friend has made this his home, I see. The uptight virgin even got himself a woman. Has he told you his name?" Molly didn't make a reply or even move. She only glared at him with all the force she could muster. "Ooh, he hasn't. How rude to ask the hand of a woman who doesn't even know his name. His name's William, darling." That elicited a gasp from Molly. The responsibility never to utter that name now weighed heavily on her shoulders.

"You loathsome creature!" she shrieked upon seeing how he enjoyed her discomfort. His murder of that poor boy was bad enough. She would not stand for any further cruelty. He only laughed at her.

"You flatter me," he giggled.

"YOU." Sherlock burst from the water like a capsized boat, fury etched in his features. Without a moment's hesitation, the other Nøkk lunged at him, but Molly grabbed him by the collar, yanking him back.

"I don't think so," she growled. He spun around and sank his fangs into her shoulder, causing her to cry out in pain. Sherlock pulled him off her and threw him into a nearby tree.

"His name's Jim, Molly. Say his name," Sherlock told her urgently before the other man could attack again. The name fell from her lips before Jim could even process that he was done for. He screamed and writhed until finally he lay dead and dissolved into a mere trickle of water.

"Good riddance," Molly muttered before she passed out.

The sun was shining in Molly's face when she next awoke and she soon realized that it was coming through the window of her cabin. Sherlock was standing over her, looking slightly concerned.

"In case you were wondering, you blacked out because of Jim's venom. My saliva fixed that problem easily enough, though," he rambled.

"He told me your real name," she blurted out and he scowled.

"Sherlock is my real name. I believe you are referring to my birth name," he told her sternly and she couldn't resist a small smile at the thought that he only recognized the name she had given him as his true name.

"I promise I'll never say your birth name," she vowed, taking his hand and kissing his palm to seal her words.

"I trust you," he said and she never let him down.

A/N: Welp. I hope that was satisfactory. If you are curious about the Huldra, I really suggest you wiki them. They're damn awesome.