First. Ellie is a borrower: a race extremely similar to humans, except for one thing. They are typically less than 5 inches tall. Borrowers get their name from their survival tactics. They "borrow" things from humans. Under no circumstances are borrowers allowed to be seen.
Second. Ellie is not very good at being a borrower. She has been seen, captured, injured, and humiliated. She was a clumsy girl, and also very oblivious to her surroundings, which is never good for someone only 4 ½ inches tall. But, Ellie's biggest crime: she "borrows" objects that people notice. This has forced her out of human homes more than once. She couldn't help but become attached to the humans that she lived around, and she wanted to keep bits of their lives for herself. From an elderly craftswoman she had taken a prized spool of golden thread; from a businessman she had bits of a Movado watch; From her last residency, however, she had only the scars and pains of abuse. She shuddered at the memory of those grubby teenage hands torturing her.
"This time it will be different," she thought out loud to herself. "I will find an easy living spot with lots of holes and untouched food. I wont even learn the humans names." A rogue borrower had led her to 221B Baker St. saying that it would be the perfect place for her. She was tired and never even thought to question the old rouges judgment.
She waited until nightfall to scale the walls and climb through an odd hole in the window. "Strange, this looks like a bullet hole." She was thinking out loud again. She tumbled her way into a very messy living room with scattered papers and unfinished chemical experiments left lying about. She wondered what kind of lives the tenants of this strange flat had. Were they scientists? They didn't look like scientists. She had watched them leave in a flurry of excitement. One was short, dirty blonde, and carried himself with military-like pride. The other was tall, slender, and completely eccentric, yet unfeeling at the same time. She had also noticed a landlady, although they treated her more like a housekeeper.
Ellie pulled her cloak up tight around herself, and went of to find a hole in the wall. She found a good amount of them; many caused by bullets, others by experiments gone wrong, and some from the the odd angry fist. There was a nice roomy spot overlooking the living room where the bullet holes seemed to be concentrated. She decided to call it home.
It had taken Ellie less than a week to deduce that these humans did not stick to a regular schedule. The shorter blonde one tried to have an ordinary life with a job and a girlfriend, but the tall dark haired one would never allow something so "boring" to happen. Despite herself, Ellie began to grow fond of the tall one. He had an interesting way of seeing the world. He could tell a persons whole life story after analyzing them for a second. He was impossibly smart, and he knew it. He called himself a "Consulting Detective" whatever that meant. It would appear sometimes that he worked for the police, but he had no uniform or badge. His clients came to him, and he often turned them down. He would only except the extraordinary, only go after villains who could not be caught, only solve mysteries claiming to be unsolvable. One name kept popping up in several cases. Moriarty.
The short one was cute in a funny way. He was so normal in contrast to the detective. She learned through conversation that he had been an army doctor, but now he had somehow become almost a babysitter to the wild man that he lived with.
The tall man had many quirks. He often talked to himself (or maybe to the skull upon the mantle). He also had viscous mood swings. One day he would be perfectly happy with his experiments and talking with the shorter man, the next he would refuse to speak and simply sit still for hours lost in thought.
The best part of 221B was the violin. The tall man played violin in a beautiful and unique way. Sometimes he would play songs that Ellie knew, and sometimes she would catch him composing. Either way she was more than happy to lend her voice, sure that it was too tiny and too far away to be heard. She watched the lives of the two men with delight, but she tried hard to keep her promise, and had not learned their names.
Ellie kept quiet and unseen for several weeks. She had learned that it was easy to steal food, despite the tall one's perceptiveness. He never seemed to eat without the shorter one telling him to do so. Food was not something that was ever missed.
Material was a different matter. Ellie learned to only borrow from the shorter man. She had taken a sock from the tall man just once, and he had noticed its disappearance almost immediately.
She continued to observe the men through her bullet hole windows, like watching a drama on the tele. As she grew more fond of them, she fell back into her old ways. It wasn't long before she had her familiar desire to steal something more noticeable.