I shall begin by apologising quite profusely for the hiatus. To those who have persisted with this story - thank you SO MUCH! And as ever I would love to know what you think.

It hadn't taken long for Merlin to compose himself. A couple of moments after his legs had given way, he had stood up once again with a beaming smile on his face, staring at Arthur as if he couldn't quite believe it. And it had only taken minutes for him to be chattering at twice the usual speed, expressing his immense, infinite joy at seeing his friend; he updated him on the most mundane things; and at last he went in for a hug, and was at first rejected, but then, after some hesitation on Arthur's part, he was squeezed more tightly than he might have liked to his friend's chest.

Sherlock watched all of this with distracted curiosity. He had to admit that it pained him, just a tiny bit, because Merlin was his acquaintance – he hadn't thought that Merlin had any friends – and he hadn't counted on having to share him with someone else. But otherwise he found himself glancing towards his phone and waiting for the display of affection to subside.

Luckily for him, both Merlin and Arthur realised the urgency of the situation, and turned back to Sherlock just as the detective was rolling his eyes in an exaggerated fashion, thinking that nobody was looking at him. Arthur looked a bit indignant but Merlin just smiled a little.

'First question,' said Sherlock: 'what is King Arthur doing in 21st-century London?'

'That's the worrying thing,' said Merlin at once. 'Kilgharrah told me –'

'Kilgharrah?

'The Great Dragon.'

'Dragon,' said Sherlock flatly.

Merlin decided to pass over that particular detail. 'After Arthur – died – I was told that he was going to rise again. In England's great time of need.'

'Really?' asked Arthur, a little incredulous.

'Really.'

Sherlock raised one eyebrow. 'Then this is England's great time of need? You would have thought we would have noticed.'

'We have noticed, Sherlock!' cried Merlin. 'Morgana – or someone emulating Morgana – has done nothing less than declare war on the country. I don't know how long we have to prepare. Seeing as Arthur is here – probably not long.'

'Do you have a plan?' Sherlock asked mildly.

It was just as Merlin was making the most indignant of faces that Sherlock's phone beeped, for the moment distracting all of them. Sherlock glanced over at the screen, and, seeing that the message was from Mycroft, deigned to pick up the phone and look more closely at it.

Have you ever heard of Lord Sebastian Moran?

Sherlock's thumb hesitated over the Google app; after a moment he replied:

He's an MP, isn't he?

Peer of the realm, and Member of Parliament for the Conservative Party in -.

And?

He's disappeared.

And?

He lives on the same street as the first victim, he has an as of yet undetermined connexion with the second victim, and he was one of the witnesses to the death of the third victim.

Sherlock blinked. He trusted Mycroft to have found a valuable lead, but he wasn't quite sure what his brother wanted him to do. He recalled, vaguely, that Mycroft had been entrusted with the job of protecting the country from whatever threat it currently faced.

You will have to investigate that lead. I have a former King of England to deal with.

This he sent to his brother without context nor follow-up; then, turning to the others, he commented:

'Merlin, does the name Sebastian Moran mean anything to you?'

Merlin shrugged. 'He's an MP... wasn't he Home Secretary at one point?... no, that was someone else... Why?'

'Mycroft thinks he has something to do with the murders. And he's disappeared.'

Merlin furrowed his brow. 'We're missing something. I'm sure we're missing something.'

'That much,' said Sherlock, a little maliciously despite himself, 'was evident.'

'Sebastian Moran,' Merlin murmured.

He might have pursued the thought further, had he not been interrupted by the minor inconvenience of the window shattering.

For a moment, time was frozen; there might have been an explosion, but none of them registered it. One moment there was a window-pane: the next, empty space and a cold breeze. It was so sudden, so spectacularly unexpected, that all present saw the entire thing happen in slow motion. The obvious action would have been for the window to shatter inwards. It didn't. As if it had merely given up on life, it collapsed from the top, creating a waterfall of glass shards that cascaded onto the carpet. Despite himself, Sherlock found himself wondering what Mrs Hudson would think. At last he managed to tear himself away from the window, to see Arthur, who had stood at the sound of shattering glass, back in the chair, having been thrown into it by the pure force of whatever had happened. Merlin, too, had staggered backwards. Perhaps Sherlock had also, but his thoughts were elsewhere.

It was over as quickly as it had begun, but it had not felt that way. Nobody spoke for half a minute. The first to react was Mrs Hudson, who, downstairs, pattered through her kitchen in a sort of panic. The second was not Sherlock, though the detective had recovered quickly from the shock, but Merlin.

The magician ran at once to the window, not seeming to notice the glass beneath his shoes. There was little left of the pane: a few fragments here and there in the window-frame. Half of the glass, it looked like, had fallen inwards. There remained to determine if the rest had gone onto the street. Therefore Merlin leant out of the window, and recoiled at once, letting out an involuntary cry.

'What?' asked Sherlock.

'We're under siege,' was Merlin's somewhat enigmatic reply.

'Under siege!' cried Arthur, joining him at the window. He had expected, at Merlin's warning, to look out and behold archers, platoons of men, siege-ladders – but the street was precisely as it was before. 'What do you mean?'

Sherlock came up behind them, and studied the scene, trying to work out Merlin's response from the magician's expression. At last he smiled humourlessly, and said: 'This is some sort of magical siege, I'm guessing.'

'It's damned clever magic,' Merlin replied, almost overawed.

'What is?' asked Arthur.

'Look at the street,' Sherlock told him.

'It looks the same as ever,' Arthur replied.

'Precisely,' said Merlin.

Arthur looked between the detective and the magician, entirely confused; it took a while, but it eventually dawned on him.

'Nobody's reacted to the explosion...'

'Are you boys all right up there?'

Their thoughts were all interrupted by the concerned voice of Mrs Hudson, who had come upstairs whilst they were preoccupied, and who now stood outside 221B.

'Yes...' Sherlock replied. 'You had better come in.'

Mrs Hudson came in, and came over to the window, and Arthur resumed speaking, voicing what the others had already guessed.

'So... someone's done something that can only be detected by people inside this building? Put up... I don't know, a barrier? An invisible barrier?'

'Very good,' said Merlin, smiling at these stumbling guesses. 'That much, at least, is obvious from this.'

And putting his hand out of the window he knocked on thin air, producing a clear ringing sound like that from a tuning-fork.

'Clever,' he murmured again, 'very clever.'

Sherlock nodded. 'It would be a reasonable guess to say that we are thus trapped in here, and that this house is the only one affected. The solution would be for Merlin to find out the counter-spell, or something that would remove this barrier. Following that we can find whoever created it, and we shall presumably have the one responsible for the string of murders.'

He felt suddenly satisfied, and couldn't quite place why. Merlin was just about to follow his instructions – to counter this sudden powerful magic with, hopefully, something greater of his own – when Mrs Hudson gave a small cough, and, looking a little embarrassed, asked of them:

'Can somebody perhaps explain what exactly is going on?'