The journey back was a silent one, full of unspoken questions and unravelling threads. Sherlock's brow was knotted; his eyes closed every so often, the rounded 'o' of his mouth frozen in position as he thought. It wasn't until they were back in the flat that John dared to say anything.

"Sherlock?" he asked, sitting down in the armchair and leaning on his knees.

"Mmm?" Sherlock was darting back and forth between his room and the kitchen, carrying microscopes and titration pipettes and chemical analysers. He couldn't have been more different to the zombie who had lain on the couch only a few hours before. The paleness in his cheeks had vanished, and, his usual confidence restored, he filled his clothes, the buttons on his jacket now looking set to explode outwards from his chest.

"The clue on the apple - 'Golden hair' - do you think it could have anything to do with..." John trailed off, searching for a word that wouldn't make him sound, well, gay. "With children's stories?"

Sherlock didn't even turn around. "What do you mean?"

"Well...the girl in the woods today. She was beautiful - oh, don't give me that look, I'm only stating a fact - and she had black hair. She was killed by a poisoned apple in a wood. Doesn't that sound familiar to you?"

"No."

Sherlock moved a stack of books onto the table, the hard leather covers hitting the wood with a thud, unaware of John staring at him incredulously. He thought it had been obvious - had he finally caught something that Sherlock had missed?

"Are you sure?"

There was no reply, and John let out a small smile. "It's Snow White, Sherlock! Snow White! The killer has modelled the murder after a fairytale."

"Snow White?"

His voice was barely a murmur, but it was loud enough for John to hear. He raised his eyebrows. "Snow White? The girl, the mirror, the evil witch?"

"Never heard of it. Help me with these books, will you?"

John stood up and was handed a large pile of medical journals. Sherlock dashed away again, his hair bouncing on his head.

Great. The one time he thought he had caught something, the one time he was smarter than a genius, it turned out to be a small lapse in said genius's knowledge. It wasn't that he had missed something - it was that, in his mind, there was nothing to miss. John shuffled on his feet and waited for Sherlock to pop his head round the door, proclaiming, "Well, John, you're absolutely right, I am an idiot, how stupid of me." Nothing. Just the empty air and the murmur of wind outside.

Sherlock finally bounced back into the room and swept up the books in his arms. No thank you, but John wasn't expecting any. "Sherlock, have you seriously never heard of Snow White?"

"Never."

"What about Rapunzel? Beauty and the Beast?" John racked his head. "The Frog-Prince?"

"The Frog what?"

"Prince, Sherlock, Prince. How come you've never heard any fairytales?"

Sherlock shrugged and sat down in a chair, his materials finally gathered. He started fiddling with a slide and a sampling of hair he must have pinched from the crime scene. "I don't know. I was never interested in them, and besides what use could they be?"

"Sherlock, you are in the middle of a case that focuses directly on fairytales! How can they not be of importance?"

Sherlock suddenly whipped round, and John shrank backwards slightly. "You are making bricks without clay, John," he said, words like venom as they left his mouth. "There is no evidence, and you need data to make conclusions. You have no data, and your mind is filled with silly stories that no one bar a child could find possibly entertaining. An apple and a forest is not enough clay, John, and if you continue doing this, your lovingly built brick house will tumble down around you. It is a capital mistake to theorise before one has data. Insensibly, one begins to twist facts to suit theories, instead of theories to suit facts. Now, leave me to my work."

Sherlock turned his back again, and John found himself fighting the urge to punch him. Instead, he curled his hands into fists and took a deep breath. "Sherlock, there's another fairytale. About a girl called Rapunzel who was famous for her golden hair. We have a Snow White, and now we have a clue that directly links to another story. I don't care what you think. I'm checking it out."

No reply. Just a steely, cold silence. John stifled a shout and turned around to grab his laptop. Picking the lightweight rectangle in his hands, he marched through to his bedroom, his pulse throbbing in his ears and his face turning a dark plum colour.

No. Sherlock could be a dick, a horrible friend and an even worse roommate, but he was not going to throw away a perfectly reasonable lead just because he didn't know about it. John would do the research - he had worked with Sherlock long enough to know his methods - and he would force Sherlock to acknowledge it. Sherlock would not be allowed to do that to him. He wouldn't.

With an angry stab, John turned on his laptop and sat it on his lap. It whirred to life immediately, and John typed in the password and waited for the background to pop up, the background and that beautiful little button that took him to the internet. Sometimes John wished he could live there permanently - there were no arguments, no annoying dicks and no violins. Just funny cats and an endless stream of blogs that could distract him from the mess that was his life.

John clicked onto the internet and stared at the screen, suddenly aware of the fact he had nowhere to start. He knew the story of Rapunzel - one of his old patients had a little girl, and he was constantly video-taping himself reading the stories - and he knew that the killer would be looking to strike again. So, setting would be helpful. It would have to be a tower...a tall one, abandoned...where could you get one of those in London?

Hesitantly, John started typing: TOWERS IN LONDON: and clicked search. A stream of sites clogged the page, but they all seemed to about the Tower of London. Well, that was helpful. Closing his eyes, John thought for a moment. Towers, towers, towers...what type of towers where there? Radio towers. Clock towers. Factory towers. Eiffel tower. Phone towers.

John froze and looked down at the screen. His fingers ran over the keys and, with a flash of adrenaline, he pressed search. Another page of results, but this time, they were promising.

ABANDONED CONTROL TOWER BOUGHT BY MILLIONAIRE- THE TELEGRAPH

RADIO TOWERS - WIKIPEDIA

BAD WOLF T.V TOWER OUT OF USE - DAILY MAIL

HOW TECHNOLOGICAL TOWERS WORK - eHOW

John moved his mouse and clicked on the third one. The article was written over a year ago, but it looked right - an abandoned tower on the outskirts of London. There was a picture and, as John enlarged it, he was once again struck by the fairytale qualities. There were vines crawling up the circular building and the sun was glinting in the round glass window at the top. A light frost sparkled around the base and a fox, its orange fur brighter than the grey around it, sulked past. The tower was perfect. Perfect for a murder based on princess stories.

Scribbling the address down, John closed his laptop and walked out of the room, grabbing his coat from the arm of his chair. Sherlock glanced up, his face as flat and expressionless as concrete. "Where are you going?"

"Out. I have a lead."

Sherlock nodded and turned back to the microscope slide he was inspecting. "Go ahead. Phone me if you find anything interesting."

John didn't reply and shrugging on his jacket, walked out the door. His heart was thumping in his chest and his mind was racing. What if the murder being a fairytale was just a coincidence? Maybe his mind was just jumping to conclusions - making bricks without clay, as Sherlock so elegantly put it. What if he came out of this looking like a fool, an idiot? What if he was wrong?

What if he was right?

Pushing the thought from his mind, John strode down the stairs and out into the cold, cold air. Cars trundled up and down the street, their wheels gliding over the icy roads. John walked to the pavement and hailed a cab, jumping into it and letting the heat caress his skin. He glanced at the cabbie - he never had been able to fully trust them, not after what happened with the pink and the pills - and said, "Tyler Road, just outside London please."

"Right."

The taxi roared to life and settling back into the seat, John wondered what he would find.

An abandoned, empty tower?

Or a stream of golden hair?