'You can't tell anyone I have magic.'

He had said it about fifty times now, and Sherlock understood completely why Merlin might want to keep his unusual talents hidden. Though it wasn't illegal – yet – to perform magic in England, he would attract far too much attention if he made it known that he could, and Sherlock knew all about avoiding unwanted attention.

But there was still one thing that was irritating him about it, and eventually, finding a break in Merlin's incessant chatter (probably some sort of nervous tic), he asked:

'If you are so intent on keeping your secret from everyone... why do you call yourself Merlin?'

Merlin grinned suddenly. 'Because it's so obvious that the truth remains hidden in plain sight. Besides, who will ever consider the hypothesis that anyone can do magic, even a man called Merlin?'

Sherlock had to admit that he had a point.

The pair had just emerged from the Barbican tube station, and were walking towards the imposing structure of St Bartholomew's Hospital. They had not continued their conversation on the Tube train, for it had been crowded, and they had been afraid of being heard, but now that they were above ground, both of them, who had before been so silent and lost in their own thoughts, found that now they did not have enough time to say all they wanted to each other. Curiosity mounted in them both: such is the situation when magic comes into the question.

But Sherlock did not like to talk, and so was secretly pleased when they entered the hospital and were reduced to silence by the long white corridors and respect for those contained within the many rooms.

Eventually they arrived at the morgue, and found two people in there; one of them, a small friendly-looking man, immediately stopped talking to Molly as they entered, and, with a brief wave and glance towards the newcomers, left the room.

Sherlock did not ask out loud who it had been, but his eyes spoke for him, and Molly laughed.

'Oh, that's John Watson. An army doctor. He's just started working at Bart's... used to study here. Mike remembers him.'

'Just returned from Afghanistan?' asked Sherlock. Molly nodded. Sherlock hesitated a moment, said very crisply, 'He's not your type,' and strode over to the waiting corpse.

Merlin, it was plain, was no stranger to dead bodies. He did not even flinch as the plastic was pushed aside to reveal a staring unseeing face and cold white skin, instead leaning in closer, studying it with a morbid curiosity. Molly uncovered the man's chest: now the mysterious burn mark was revealed.

Merlin fought back a shudder that began to crawl down his spine. He studied the wound for scarcely a moment, and then said: 'And you say that the other man had the same injury?'

Molly and Sherlock both nodded.

'Do you know what it was caused by?' asked Molly, nibbling her lip a little.

Merlin exchanged glances with Sherlock. The detective furrowed his brow, and then nodded slightly. Not entirely reassured by this response, Merlin turned back to Molly and said:

'Yes. I do. It was caused by magic.'

Molly, of course, looked completely incredulous. Her eyes widened, and she looked to Sherlock as if hoping that he, too, found this response ridiculous. But the detective seemed to take him seriously.

Molly tried to laugh it off. 'Oh, come on, magic doesn't exist. If you don't know, it doesn't –'

At this Merlin, with scarcely a blink, reached forwards a little and plucked a small red tulip from thin air. He presented it to a slightly baffled Molly, who did not take it.

'Magic exists,' Merlin said, very simply, 'and if I managed to persuade Sherlock that it does, then I can persuade you. I can understand if you're sceptical. You just have to – suspend your disbelief for a bit. If I tell you that magic caused this wound, well – I know whereof I speak.'

Molly stared at him. Then at Sherlock. Then at Merlin again.

'I speak as a survivor of the same spell that these men suffered.'

It was hopeless. Molly, more rational, it seemed, even than Sherlock, did not in the least believe him. Reluctant to show her any more proof in the relatively busy atmosphere of St Bart's, and slightly regretting telling her to start with, Merlin shrugged and said:

'In that case, just promise me you won't tell anyone what I said, or – what I did.'

And, with a small smile, he pressed the tulip into Molly's hand and left the room.

They had just caught the Metropolitan line service, and were speeding back to Baker Street, when Sherlock's phone buzzed. He slid it from his pocket, read the text message that had showed up on the screen, and, without a word, passed it to Merlin.

Parliament Sq Gn. Come and look at this one. Bring Merlin. Greg

'Greg –?'

'Lestrade. The detective inspector.'

A change and a short detour later, the pair found themselves just across from the Houses of Parliament. The large lawn behind the famous building, which was flanked by statues of various noted politicians, and which was usually filled with tourists, had been cordoned off; there was a line of police vans and cars around it, and the tourists were being kept a good distance back, on the opposite side of the road. Sherlock presented his I.D. to one of the police officers on the edge of the cordon, and they both hurried to whatever was being concealed at the centre of the garden.

It was another corpse. Sherlock had expected that. He hadn't, perhaps, expected it to be so grossly disfigured as to be almost recognisable as human. The man – if it was indeed a man – looked as if he was suffering from some grotesque disease that caused excessive amounts of skin to grow from his face, his arms – everywhere that was exposed, indeed.

'What –' Sherlock could not finish his sentence.

Lestrade swallowed. 'Exactly. The witnesses,' he glanced towards one of the vans, where a woman wrapped in a blanket was sobbing into the shoulder of one of the policemen, 'all say that he didn't look like this before – before he started flailing around and collapsed. That woman over there turned him over and his face had gone like that. He seemed to have died almost instantly.'

'And the connexion to the others is – what?'

Lestrade, leaning over, very carefully rolled up the corpse's sleeve. There on his arm, the word MERLIN had been etched into the skin – just before death, it seemed, judging by the rudimentary scab that had just begun to form.

Sherlock winced, and turned away for a moment. It was then that he saw that Merlin had hung back, standing to one side, and was too far away to see any of the mutilation to the corpse.

'Merlin,' he called. 'Merlin, we need you.'

Or rather, whoever killed this man seems to need you, he could not help but think.

Merlin ran over – and almost fell over backwards when he saw the corpse. His expression then was one of the utmost astonishment and terror.

'What is it?' asked Sherlock urgently.

'I've seen this before,' said Merlin in a strangled voice. 'Before – when –'

'What?' asked Lestrade.

'It's a declaration of war,' Merlin stammered out. 'And the trademark of – no, not her –'

'Who? Who's her?' Sherlock insisted.

'You know some of the legend of King Arthur, don't you?' Sherlock nodded after a moment. 'Well, do you remember Morgan le Fay, also known as Morgana?'

'...Yes,' Sherlock and Lestrade said, almost at the same time.

'Well,' said Merlin simply, 'her.'