Sherlock was breathless when he at last arrived at the door to 221 Baker Street. He had run after Merlin, believing that the boy would be unable to match his own remarkable speed, only to find that Merlin was rather faster than he had expected. He had entered the flat and closed the door even before Sherlock had reached the step.

Trying to hide the fact that he was short of breath, the detective raced upstairs, to find Merlin sitting calmly in his armchair, his dusty old tome opened on his lap, absorbed in the browned fading writing.

'Merlin –' Sherlock placed his hand on the doorframe to steady himself. 'What was that about?'

He flicked his eyes upwards. 'England's in danger. I'm the only one who can stop it. I didn't want to panic anyone so I came back here before they asked questions.'

It was this statement that made Sherlock suddenly overwhelmingly curious about the book, but, also from this statement, he caught Merlin's wish to be left alone. His hand slid slowly down the doorframe. Merlin shot him a final glance before disappearing back into his book.

The text that Molly sent Sherlock later that day, just as she was going home from work, informed him that the damage to this second corpse was exactly the same as that to the first. Nobody had yet worked out what had caused the horrific burns that, furthermore, seemed entirely unnecessary.

The working hypothesis was that internal damage sustained by the wounds to the head, or the fall that the victims seemed to have taken, had been the cause of fatality. This, of course, was not remotely satisfying, but unless an alternative was found, that was all they had to go on.

Sherlock wondered whether to share the results with Merlin, but, as he entered the living-room, he found the boy still deeply engrossed in his book. He wondered whether that was what he himself must look like when he lost himself in his mind-palace. Knowing that he wouldn't like to be disturbed in such a state, he left Merlin alone, made himself a cup of tea, and came to sit quietly in his own armchair.

It had not, of course escaped Sherlock's attention that Merlin seemed to know more about the case than the rest of them. He recalled the strange message, which the boy had pocketed on running from the crime scene. He recalled the bizarre suggestion that this Merlin was, indeed, the one referred to by the note and by that curious graffiti. If that was true, it would hint that Merlin was mixed up in the series of crimes.

He was not, however, the perpetrator. He had been genuinely astonished by the appearance of his name, by the note – the fear on his face said that it was some enemy of his who was working against him. Sherlock wanted nothing more than to question him, to get to the bottom of this ridiculous matter –

'Evening, Sherlock,' said Merlin, emerging quickly from his reverie.

Sherlock started. He had been himself slipping into a bit of a daydream. 'Ah. You've finished. I need to ask you –'

'About my involvement in the case?' Merlin said with a hollow chuckle. 'I don't know myself. Not yet. All I know is that all of these events are a warning.'

'A warning of what?'

'A storm on the horizon...' He left this poetic line hanging in the air, which was crackling a little with anticipation.

'Can't you at least give me a straight answer?' Sherlock said, exasperated.

'You wouldn't believe me if I told you the whole story,' Merlin shrugged.

'Try me,' Sherlock said.

'It's not very probable,' Merlin said lamely.

'In such a case as this, when you've eliminated the impossible, whatever remains, however improbable, must be the truth,' Sherlock said. 'There is little I won't believe.'

'Do you believe,' said Merlin, and faltered a little, 'in magic?'

'Magic,' said Sherlock flatly.

'Magic,' Merlin repeated, unfazed.

'Don't be ridiculous,' Sherlock said.

'You said you could believe anything –'

'I said that there was little I wouldn't believe. Not nothing.'

'And why isn't magic believable?'

Sherlock could not help but scoff. 'It's the stuff of fairy-tales. It goes against the laws of physics. The laws of nature. It's an invention, a simple invention to make stories more interesting, or to fuel the wild fantasies of –'

'Can you disprove it?' Merlin asked, cutting him off.

Sherlock furrowed his brow and did not reply.

'It's far easier,' Merlin contemplated, 'to prove something than to disprove it. You cannot show me a lack of evidence for the existence of magic. I however can show you evidence for its existence.'

Sherlock could not help but agree utterly with his logic. The man was turning out far more intelligent than he had at first assumed (which wasn't, to be perfectly honest, saying much). Yet he still could not help a small incredulous smirk coming onto his face. 'Very well. Show me your evidence.'

Merlin raised one eyebrow, giving his face a rather mischievous look that Sherlock wasn't sure he had expressed before. 'One thing: confirm to me that magic isn't against the law.'

'I doubt there are even laws in place that take magic into account,' Sherlock replied, a little drily, after a moment.

'And if it was,' Merlin said, his voice becoming a little more serious, 'would you report me for what I am about to do?'

There was some primeval worry within that voice, something bordering on panic, that Sherlock found himself drawn by. Merlin was turning out to be an enigma. And he hadn't even done any magic yet.

Swayed by this very curiosity, Sherlock said, 'No, of course not. Now prove the existence of magic to me.'

He could scarcely believe he'd said it, he could believe it even less when Merlin, now deathly serious, placed his book on the coffee-table and stood. After a moment of contemplation he removed his jacket. Sherlock reckoned that this was just for dramatic effect. The jacket fell onto the chair; Merlin straightened, turned, extended his arms towards the dry and dusty fireplace.

Sherlock's eyebrow twitched. He guessed what Merlin was about to do. He vaguely registered the absence of wood in the hearth.

And, without warning, Merlin began to speak in a low and carrying voice; the air in the room crackled; he released his hold on the words, on this apparent spell, on the magic within him –

A fountain of blue flames shot up from nowhere, spreading their tongues far up the chimney before settling in a shower of sparks to a warm golden orange. They seemed to hover in the air, for there was nothing to fuel them but whatever Merlin had produced.

Sherlock felt a little faint. He put it down to the heady, suffocating atmosphere that seemed to linger for a moment before dissipating into nothing. Merlin, entirely unaffected, turned to gauge Sherlock's reaction.

He did not even need to ask him what his opinions were on the matter. Sherlock, normally so reserved, now wore his emotions on his sleeve. He looked utterly astonished. Perhaps he even looked a little admiring, despite himself.

'Whatever remains,' Merlin said, with a small grin, 'however improbable, must be the truth. Magic exists, Sherlock. You'll need to fit it into your hypotheses.'

'Yes,' Sherlock said vaguely. 'Yes, evidently.'

And though he felt greatly exhilarated and satisfied by what he had just seen, he could not help but feel as if things had suddenly got a lot more complicated.