It happens so fast Merlin doesn't even think about it. They are in Gaius's chambers, because Arthur wanted to look through his books for a solution, Merlin not having found the courage to tell him the truth yet. The vial filled with liquid begins to fall, his head turns, his eyes fixate on the plunging object, he holds his breath for a heartbeat and the glass smashes to the floor anyway.

'Oops,' Arthur says, glancing over his shoulder and then to Merlin with a slightly apologetic smile. But Merlin still stares at the broken shards, the yellowish liquid seeping onto the tiles.

'What?' Arthur asks him, closing the book and putting it back where he found it. 'Was that something really important? Or valuable?'

'No, it's just-. I-, eh think it's a sleeping draft. No matter I'll clean it up.' He spins around to look for a cloth but his eyes frantically move from the left to the right. It didn't work. Why didn't it work? Grabbing the cloth he bends down, mops up the liquid and then carefully picks up the broken glass. When he is certain Arthur isn't looking, he glances down again, whispering something under his breath, but the familiar heat doesn't flicker across his eyes and the vial remains broken. A heavy, creeping panic starts to rise from the pit of his stomach. It works its way up slowly, until it bubbles into his throat and his breathing quickens. Merlin's shoulders start to rise and fall in rhythm with the halting, irregular breaths. 'It is gone,' he thinks. 'My magic. It is gone.' But then…

At that moment the door opens and Gaius steps inside, his eyes first finding who he thinks is Merlin, still standing by the bookshelf. 'Ah,' he begins, no doubt about to give him some task, but then he notices Arthur rising to his feet and his eyebrow worms its way toward his hairline. 'Sire,' he observes. 'You are here. Again.'

'Yes. Eh, hello Gaius.'

'Is there something I can assist you with?'

'No, eh not at all.' Merlin says, edging his way toward the door, still clutching the wet cloth with the broken vial. Arthur starts to go after him, with Gaius's frown following them both.

'Wait a moment,' he tells them finally. 'There is something very odd about all this. Merlin, what is going on? Why did Arthur just clean something up from the floor?'

'Well eh…' Arthur begins, shifting a wide eyed look between Merlin and the physician. 'I-, he dropped it. It's only fair…'

'Merlin, you are the servant. This is outrageous!' he turns to who he thinks is Arthur. 'Sire I apologize,' he offers while taking the cloth and glass out of his hands, and then twists back to who he believes to be Merlin. 'Go and fetch fresh water for the prince at once, so he can wash his hands, they are all sticky.'

'No I assure you,' Merlin begins, stepping forward, but Gaius holds up a hand. 'I insist.' He adds under his breath; 'Merlin, now.'

Merlin sees Arthur gnash his teeth briefly before turning to the door and stalking through it.

'Honestly Milord, I don't know what is wrong with that boy late-.' Gaius stops talking in astonishment when the crown prince grips his wrists and pulls them insistently.

'Gaius,' he hisses. 'It is me!'

'Well, yes,' Gaius tells him, pulling back a little. 'I can see that.'

'No it's me! Merlin!'

'Wha-' Gaius half laughs, sure this is a joke.

'I'm serious! Something happened, Arthur didn't want me to tell you but we have no choice now! The dragon told me about Magical Winds or whatever and now are minds have been swapped!'

'Good Heavens,' Gaius mumbles and sinks down on the bench. 'Merlin?' he asks in a weak voice.

'Yes.'

'Oh no. Did I just order the prince to fetch water?'

Merlin presses his lips together in what is meant to be a sympathetic gesture. 'Yes.'

Gaius buries his face in his hands for a moment. 'And I made him rub my feet the other night, didn't I?'

'Yes, I do believe you did,' Merlin snorts, clapping a hand in front of his mouth.

'It's not funny Merlin.'

'No, you are right. But that's not the worst thing,' Merlin hisses. He knows he needs to be quick, Arthur could return any moment. 'I don't have my magic anymore.'

'What?' At this Gaius's head snaps up. 'Merlin…'

'I know, it must be bound to my body somehow. But how is that possible? Surely magic is in my mind, because you can learn it. Right? I mean… Maybe I'm just a little confused and…'

'No Merlin. You were born with it. That is very rare. For all we know it is in your blood. Which means-.'

'That it is in Arthur's blood right now.'

They stare at each other as they imagine the implications. But then heavy steps can be heard outside the doorway.

'There is something else you should know Merlin!' Gaius tells him, talking fast and under his breath. 'I have heard of this sort of magic before, if something happens to one of you - if you should come to die - the other will die too. There is still a link between your own body and mind, and one cannot live without the other.'

The door opens.

'You have to pretend you don't know!' Merlin tells Gaius quickly. 'For now.'

'What? I can't…'

But Merlin already pulls away from Gaius, putting a more appropriate distance between them and Arthur steps inside with half drenched trousers.

'Thank you!' Merlin tells him, hurrying forward and taking the bowl out of Arthur's hands. He glances down. 'Something happen?'

Arthur gives him a look that could make the sun set early, remembers Gaius's presence and just huffs out something unintelligible before disappearing into Merlin's chambers. Gaius frantically points at Merlin, then at the door, then at his own head and when Merlin cocks his head to the side with a quizzical look, he just rolls his eyes, shaking his head. 'You have to do someth-,' he begins, but the door opens again and Arthur reappears with dry clothing.

'Didn't you say something about needing to go back to your chambers, Milord,' Arthur says icily, widening his eyes in what Merlin thinks is meant to be a meaningful way but just makes him look a little deranged.

'Yes. Yes, quite right.' He gives Gaius a I don't know what to do, I'm just rolling with it sort of shrug and follows Arthur out of the door.

'Merlin, I have had enough! This has to end today.' Arthur complains too loudly for the castle corridors and Merlin has to whisper an insistent shush when a servant girl's eyes widen in shock.

'Actually, I managed to have a peak at that last book you picked up while you were changing into dry clothes,' Merlin lies. He doesn't like lying, especially to Arthur. He sort of hates it in fact, but he is fairly certain he'd hate having his head chopped off even more.

'Oh?' Arthur says in encouragement when Merlin doesn't finish his sentence. He opens the door to his chambers and without thinking holds it until Merlin steps inside.

'Yes. It was the correct book.'

'Course it was,' Arthur smirks, regaining some of his old swagger. Merlin pretends he can't hear him.

'It describes a case where something similar happened, purely for scientific research of course,' he improvises, not wanting to get Gaius into trouble because of his lies. 'And the effects wear off automatically-'

'They do?' Arthur's eyes widen hopefully.

'Eventually.' Merlin finishes.

'How long?'

'Eh- it varies.'

'How varied are we talking?'

'Days, weeks at the most.'

'Weeks? Weeks?'

Merlin knows that look and starts to talk very fast. 'Before you start throwing things at me, it's not my fault and now at least we know it isn't permanent and remember this is your head you'll be throwing stuff at!'

Merlin is reminded of a nervous racehorse when Arthur exhales a loud breath through his nose. 'Right.' Arthur tells him, running a hand through his hair. 'I am not spending one more night on that haystack of yours, or rubbing feet for that matter, knowing you are sleeping in my bed!'

Merlin's lungs deflate as he hangs his head, suspecting what's coming. And he is right. 'We are going on a hunting trip. Pack my things, we leave straight away.'

Merlin casts a last mournful look at the bed before turning to Arthur's wardrobe.