Disclaimer: I don't own the rights to BBC's Sherlock or Sir Arthur Conan Doyle's Sherlock Holmes or anything like that.
The biggest secret kept by fairies is their ability to shift their physical form in almost any way they wish. Even when humans did believe in fairies, they could only guess at the true extent of the magic harnessed by the winged people. Very few fairies however, choose to change their form because they generally feel uncomfortable in forms that are not their own. Molly however, was one of the few exceptions to this generalization.
The biggest drawback, to Molly's mind was the amount of magic required for such a transformation. An illusion like that of a fairy shape-shifting into a humanoid form could drain a fairy of their magic, which was extremely dangerous. If a fairy used up all of their magic then the best they could hope for was to simply become mortal; though that almost never happened. Spells tended to have the unfortunate tendency to run amuck if not properly controlled, which could spell disaster. There was one way around that though: a talisman. A talisman could store enough magic to power a spell for longer than a fairy might otherwise be able to on their own.
The talisman that a fairy chose would stay with them throughout their lives and help them with many difficult spells. Because of this, there was a large celebration every year when it came time for the newest brood of fairies to choose their talisman. Molly had been so excited during the party that she had almost dropped the locket that she had chosen several times. Most fairies didn't pick something that was almost bigger than their head, but it was the one object she had kept from her past adventures in the forest that could blend into the human world. And besides with a simple enchantment the locket could be shrunk to fit Molly perfectly.
Molly enjoyed walking among the humans. To most of the fairy people, humans were simply dull and weak. This was of course the natural side effect of immortality and spell-casting, and the point of view that such power could give a person. However, there was one boy who came out into the fields often and every time she saw him, the boy grew more and more interesting. He seemed to be trying to absorb every minute detail of the world around him, unlike most mortals who simply saw and then moved on.
This intrigued Molly so much that by the time the boy had reached his late teens, she decided that she must talk to him. So one morning when he had found his way back to the field where she had first seen him as a little boy, Molly hid herself behind a human form - one of her favorites, a young girl with long brown hair, barely sixteen - and began wandering through the fields towards the boy. The day was so beautiful that it made Molly giddy. The sky was a seemingly impossible blue and the sun shone down on the small clearing made by a circle in the trees that were otherwise blotting out the surrounding skyline.
The boy was so busy cataloging the newest spring flowers and wondering what the best way to transport some of the petals, or perhaps a whole flower, was without them being crushed, to notice her as she headed towards him. She wondered if she ought to say something so she wouldn't startle him, but was saved the worry as the boy stood suddenly and turned toward her. They stood for a moment, staring at each other
"Who are you?" he asked, his angular features twisted into a quizzical, yet somehow demanding expression that caused Molly to giggle.
Sorry," she apologized, still giggling. "My name is Molly."
"Sherlock." He introduced himself and that was the last shred of attention he gave Molly as he turned back to the patterns in the dirt beneath his feet.
With an unpleasant lull in whatever conversation there had been and no idea what to do, Molly found herself staring at the boy. She had been led to believe through the stories of her people that most humans were more than willing to talk to a fairy – though they never knew the true identity of those they were talking to. It was believed that the magic fairies used to keep a human-like form also enchanted the humans, but with this boy this hardly seemed true.
It took nearly two minutes for Molly to recognize Sherlock's growing agitation. She had simply been watching as he saw the world around him, and had not really thought about the passage of time until the boy sighed dramatically and turned to her. "Why are you still here?"
"What are you doing?" Molly countered with her own question and walked towards Sherlock, bending down to see what he was looking at.
Sherlock didn't answer and was about to pick up the bell-shaped purple flowers in front of him – intending to take them home – but a loud shout from Molly made him stop. "What is it?" he asked irritably, turning towards her.
"Those flowers are poisonous. If you want to pick some wildflowers, then you want the white bunch over there, or almost any flower but those." Molly motioned to a clump of daisies and then around the entire clearing.
Sherlock stood looking over Molly for a long moment. He seemed to be thinking rather hard about something but seemed to give it up before questioning her. "How do you know that?"
"I. . . I just do," Molly stammered. In truth, she had known this since she was just a little girl. All fairy people had to know which flowers were safe and which were not, and Molly had wrongly assumed that all humans knew the same.
"Tell me more," Sherlock demanded.
Just as he did, Molly could feel the magic surrounding her waver. The locket –her talisman- was draining faster than she had anticipated. "What?" She had been too caught up in her thoughts to hear Sherlock. "I'm sorry. I have to go – I will be back here tomorrow." She added the last comment in a rush. She wanted to see this boy again, to talk to him again, and hoped he felt the same way.
Molly just made it to the trees before she had to break the spell. The locket had used its entire store of magic and she could not hold the illusion any longer. Back in her true form, she found that her wings were a little stiff from disuse, but she flexed them a little and heard the reassuring whishing sound that let her know everything was in working order. It took her a moment to locate her locket between two trees where it had fallen as she shifted back to her true form. Then, once she pulled it out of the dirt, she quickly shrunk it so that she could carry it up to a space between branches in the closest tree.
She sat on a branch not more than four feet off the ground watched interested, as Sherlock picked a bunch of flowers, carefully avoiding the ones she had told him were poison, and then walked off in the direction she assumed his home was in. She continued to sit for a while. She enjoyed taking in the day around her and nature's energy as she thought about the human boy she had gotten to talk to today, and she had no desire to go back to the village just yet.
Sherlock had been about to repeat his request –demand- for information, but the girl was already gone, running to the closest clump of trees. He could not make sense of why the girl – Molly, he kept reminding himself – had run off so quickly. That alone made up his mind for him: he would be back in the clearing the next morning. Until then, he decided he was ready to be inside, perhaps reading. He followed Molly's instructions on the flowers and picked a safe-looking bouquet for his aunt.
As he thought over his previous conversation with Molly he thought about how he had taken to studying plants out here because there was little else for him to do. However, in all of his time out here he had not thought to learn if any of the flowers were dangerous. Who was this girl and how did she know about the flowers? If he had no thought to learn about them then he was sure that very few other people would have. Those questions weighed heavily on Sherlock's mind as he walked back to his aunt's cabin.