Disclaimer: I don't own or am in any way associated with BBC's Merlin, I just borrow the characters for fun and make no profit with it.

Spoilers for all of season one and none for season two.

Advantage

It's Merlin's blatant lack of distraction that tips him off.

It's been ice-cold for weeks. He's been on patrol much longer than usual, because some of the ways are too iced to trust the horses on them, and they had no choice but go by foot; and despite of the warm clothes he wears underneath, his armour's been feeling like he's clad in ice.

He distantly remembers Gaius saying something against this, but he doesn't care, orders a hot bath to his chambers as soon as he's back; and it's a good plan, insofar as he's not planning on standing around in front of the tub naked testing the temperature. Instead, he quickly removes a long-sleeved woollen shirt, first layer of clothing, and throws it to the flow, and pauses in his movements when Merlin immediately retrieves it and disappears in the back of the room, doing something indistinct by a drawer.

The truth is that Merlin isn't so much a bad manservant – alright, he is insofar as he's hopelessly disrespectful, needs to be told everything instead of anticipating, forgets things, and has trouble with the notion that he can't just vanish whenever he's not needed, but he's not actually bad at what he does, and he does follow orders, even if it's not without complaining – as one who goes about his chores in a constantly distracted way that gives you the unpleasant impression that serving you is a pretty minor part of his life, which, frankly, is rather insulting. He's not diligent and concentrated like this, it simply doesn't happen. It's been months, and sometimes Arthur still half-expects him to come out with "that was funny, but now where's my real reward?"

Hopefully not to Uther.

Now that he thinks about it, he really should have noticed. He slowly half-turns, so he can actually see Merlin from the corner of his eyes. He can't remember doing anything that could have annoyed Merlin lately, but he's been on the edge and probably took it out on him. Most servants do this kind of thing, he knows (though not to him, of course, because he's Arthur Pendragon), but only Merlin is so utterly careless about it.

"Merlin?" Arthur calls.

Merlin turns round and looks at him with very wide eyes, seeming to try to radiate surprise and unconcern at being called, and failing.

"Hm?" he says.

"Come here."

There's a short pause before Merlin obeys, approaches cautiously and without taking his eyes off him, ready to flee at any sign of –

As soon as he's in reach, Arthur grabs him, pulls him over, shoves him underwater up to the shoulders, holds on firmly despite of the violent thrashing, and drags him back out by the hair.

Merlin staggers a little, still slightly bent, relying on Arthur's hold on his hair for steadiness for a moment, and coughs abundantly. Icy water is dripping from his hair. Arthur lets his hands drift down to the back of his neck, feeling the skin shiver under his touch.

"Cold?" he offers, with a sarcastic sideway look.

"We –" Merlin manages, after another few coughs, and interrupts himself to snort small droplets of water from his nose, and blinks quickly a few times; Arthur tightens his hold, hand just bellow the back of his neck, when Merlin tries to straighten up. "We're low on firewood."

Ah. That explains and excuses it then, aside from the bit where he hasn't been warned about this, and the bit where the water is way bellow room temperature.

Merlin gives him a cautious look from the corner of his eyes.

"Er... Can you let me go now?" he asks hopefully.

You'd think that with the imminent threat of submersion in icy cold water hanging above – well, beneath – his head, even Merlin would remember to address him properly? You'd think wrong. He hesitates, and tightens his grip again when it seems like Merlin, for all he looks cowed at the moment, is about to try and force the issue; he's really tempted not to, but if there's no way to properly warm up, this might actually be dangerous, so in the end, he lets go.

He lets his hand sink and steps back; Merlin quickly backs away from the tub, just in case, rubs his eyes and glares at him. Arthur wonders: he has no idea if Merlin can move water the way he apparently can solid objects, but there's the tub itself... And he highly doubts that Merlin lacks imagination, when it comes to something like that.

Not this time though, it seems.

Instead, Merlin gives him a petulant look, but bites down whatever remark it is he has on his lips, and walks to the door.

"Where do you think you're going?" Arthur calls at him, and throws a towel at his head when Merlin turns round.

Merlin unenthusiastically rubs his hair, and snaps:

"Someone told me they want their horses tended to."

"Do it later. You can't go outside with wet hair, you'll get ill," Arthur says easily, and sits down on his chair; he can still take a bath later, when the water is at least at room temperature. "You're the physician's apprentice, you should know that much."

"I – I can dry it," Merlin says, while squinting at him, like he isn't sure if this is a kindness or the exact opposite.

"How?"

Merlin opens his mouth and closes it again; magic, of course, but he can't say that.

"And take off that wet shirt." He stands up and walks to his cupboard; a pair of trousers falls down when he opens it, because Merlin isn't all that good at stuffing it. "You can borrow one of mine. Wash it after."

Merlin grimaces.

"I'll be fine," he complains. "I'll never finish work if I stay here doing nothing."

"Who said anything about doing nothing?" In one quick gesture, he makes most of the cupboard's content tumble to the ground; from the corner of his eyes, he can see Merlin's mouth gap open. "There." He turns to his manservant with a smirk. "Clean it up. Properly this time."

He walks back to his chair; Merlin glares at his back with so much heat that you'd think he'd catch fire if looks had such a power; but his shoes don't rebel beneath him and send him tumbling to the floor, and the clothes don't fold themselves on their own, and after a long, long silence, and a muttered "prat", Merlin kneels down by the pile of clothes and goes to work. Arthur sits down and discreetly observes him with a found smile on his lips.

He's noticed something on the very first day.

Not the magic, of course; nothing he knew about sorcerers then had led him to believe they could do something at the same time so subtle and so open. In Camelot, you practice magic either in the greatest secrecy or in a way that offers a fair chance for you to win against the forces you're faced with; but you don't push around boxes to make the Crown Prince bump his knee in the middle of a crowded market place because he's made fun of you. At the time, he just thinks he's been remarkably careless, and Merlin remarkably lucky.

What he does notice is the way Merlin holds himself as he challenges him, with a strange kind of restrained courage, and he's intrigued. He mentions it to Morgana, later, in what he supposes is a moment of total brainlessness: she remarks, raising her perfect eyebrows at him and smiling, that he sounds like he's infatuated.

He thinks nothing either, of the incident with the chandelier that saves his life, though, in retrospective, he thinks he really should have. At the time, he's busy being shocked by the way his father chooses to reward Merlin for saving his life; can't he give people a place in his own household, if that's how he wants to do things? But Merlin stares back at him with equal dread, and he feels a little better: clearly, he does not realise that this is an honour, and thus he's not going to act like it's a honour he's owed – which would have been a good excuse to get rid of him again very fast, but then, Merlin is intriguing.

What is definitely suspicious is the way Merlin, who stumbles around, thoughts elsewhere, half of the time and is slow whenever he's under Arthur's gaze, manages to do chores he can take home with him with impressive speed (not that Arthur is going to tell him that). He doesn't notice that, at first, either, because he isn't giving the workload his manservant is dealing with much thought, but once he ends up paying attention to Merlin, it's flagrant.

He learns to read Merlin's reactions, small, but easily noticeable once you are looking for them, and certainly interesting: telling him to muck out his stables, which alright, is seriously annoying work but shouldn't take the whole day, earns him a tirade of complaints; an absurdly long list of sewing to do in an absurdly short time only an annoyed eyeroll; sending him, repeatedly, to get something from the other side of the castle results in a murderous glare at the beginning of the week, and only a deep, resigned sigh five days later; ordering him to throughout clean his chambers on a beautiful morning when it's very obvious Merlin just wants to be outside doing whatever it is people who aren't allowed to hunt do outside only gets him a not even particularly viciously muttered "prat", while informing him that he'll be lying in bed watching him work achieves a furious tensing of the whole body, pale fists clenched in anger.

There's definitely something going on there.

Valiant, and Merlin's action there are – something he'd rather not think about; he makes a generous attempt at getting Merlin a drink for his troubles ("I get to drink the left-over wine I carried up here, and that's supposed to be a present?"), and doesn't mention it again; and when they visit Gaius' place in search of the sorcerer, he goes to Merlin's room himself, lets him come after him, doesn't look as meticulously as maybe he could have, doesn't want to know but won't look away if he does.

He only half-admits this to himself; it's Merlin confession that makes it all click into place for the first time, he can't hide from something as obvious, and he's been shirking his duty to keep him from suspicion and the idiot thinks he can ruin this for him!

He has to keep up the pretence of lightness, but he does hiss at Merlin menacingly once, staring at him, but this being Merlin, of course he completely misses the underlying message (don't you dare do something like that ever again and if I want you on the executioner's block I'll drag you there myself and this is not your fault and what are you doing here anyway, I'm sure I gave you something to do) and just stares back with unconcealed anger, and if the situation were any less serious he'd enjoy this. The council smiles at them indulgently, and Arthur feels that after this, they will require some convincing that Merlin is sorcerer if he does magic before their very eyes – which he doesn't try, funnily enough.

It's the fight on the same day that confirms his suspicion for good: fire blazes from his torch, he has to close his eyes and turn away from the heat, and the sound of the creature burning covers Merlin's voice – but he notices anyway; if there were any doubts left (that the fire reacted to the creature on its own, that there's someone else here, that this is Morgana), a quick look at Merlin's dangerously unguarded face right after would have eased them: he looks elated and proud and astonished. Maybe it's the first time that he has done something like that.

He says nothing. Merlin is a sorcerer, but even if he has acted only out of concern for his friend, he has saved not only her, not only him this time, either, but Camelot, which would have fallen without water: for this, he can betray even the king his father without guilt (he would have born the guilt anyway, he privately suspects, and to some extend does because logic does nothing for feelings: but this makes it easier).

He doesn't make Merlin practice with him only because it's fun to see him stumble around and fall to the ground, even though yes, that is part of the reason.

Part of it is for his own practice, even though Merlin wouldn't – doesn't – believe it when he tells him: Merlin is in no way an adversary for him, but it's a way to practice certain moves, as with a simple, motionless dummy, or nothing at all, in a way he doesn't like to with his knights, because there, practice is always more about training them.

And, the other part, the one that's growing more and more important, even though he wouldn't tell Merlin this, is about teaching him as well: Merlin, of course, thinks he doesn't need it, but Merlin is an idiot. Magic is dangerous, magic can get him killed; it will be good for him to be able to defend himself without it.

That isn't to say that it isn't fun, of course; Merlin is, actually, in many ways an exemplary subject, what with the willingness to die for his liege – and Arthur will get back at him for that, and no, risking his life getting him a flower for the antidote doesn't count, Merlin was unconscious the whole time, didn't get to worry – but he just can't shut up; coming at him with a raised weapon is still the most effective method Arthur has found. Of course, he tries to talk anyway, talk him out of it, but it's easy to leave him no time for it. It's stopped being about making him behave like a proper servant after the very first time, or maybe even half-way through that one; it's something else now. He doesn't know what exactly; only that it's important. And fun, on a completely different level, simply because spending time with Merlin is, and by the time he acknowledges that, he's too far gone to even feel it shouldn't be.

And maybe, a little bit, he hopes that Merlin will slip, just like he did, he's sure of it now, the first day they met.

Ironically, it's his father trying to steel him against sorcerers that eases his worry; "to know one sorcerer's heart is to know them all", he says, and Arthur can vividly see Merlin's wide, frightened eyes and the resigned look on his face as he raised the poisoned cup to his lips (he should have stopped him, should have trusted him enough to stop him), remembers the blue light that guided him (and it's like he can feel Merlin in the gentle glow, who else? – But maybe it's only because it's what he wants, so much), and knows his father is wrong, has been wrong all along. Knows that Merlin, who can make a torch blaze to a burning storm and still fumbles clumsily with the firestones in front of his chimney one day out of two under his amusedly despairing gaze, is nothing alike Nimueh.

"You should have told me: magic is dangerous, you know that."

Never did Merlin come this close; he waits for it (hopeful, eager to an amount that's frightening), but it turns out differently.

It's only much later that he realises that his warning could have been taken in a completely different way: to means danger for others, not for the magic-user himself within Camelot. But by then, the moment has passed. And it's up to Merlin to find a new one, not him.

"You cannot trust a single word a sorcerer says."

He would feel guilty for this one, said in anger, if he weren't certain that the badly concealed glee with which Merlin advises him to act behind his father's back and seek out the sorcerer is a kind of revenge. He doesn't begrudge him this, either; Merlin seems surprisingly good, all in all, at not really hating Uther.

But maybe he is a little angry about Merlin's silence, after all.

"You don't have any natural talents, do you, Merlin?"

It's in all vain. In this, Merlin cannot be provoked, it appears.

And that's a good thing, of course. It means he's safe, even if it does sting a bit.

"And I owe it all to Gaius."

He doesn't know what Merlin did to save him from the Questing Beast's bite; but that it was his doing, he has no doubt.

There was a time when all his servants were respectful, efficient, and quiet, and at least the latter would unsettle him by now; it's an a bit worrying realisation: he's getting used to getting used to Merlin, but there's no reason to getting used to having an incompetent manservant too.

But he's glad, immensely glad, before he even knows why, to wake up to the sound of Merlin rummaging through his room, setting breakfast, dropping things, putting things aside, walking in an uneven pace.

Then he remembers. Worry and relief come at him at once, and don't seem to quite cancel each other out. He remembers Merlin's words, the day before, how strange he was; but Gaius had given him something for his pain that made his head swim, and he'd been so sure that the danger was over and –

And Merlin had bidden him farewell, that evening. Merlin was expecting to die.

And he's here now.

"Merlin," he says, before he even opens his eyes, and he hears Merlin pause, then walk closer to the bed; "where were you yesterday?" he adds, and opens his eyes at last, a little worried still, and thus too distracted to think of a task that he absolutely needed Merlin to do the day before, when Merlin wasn't there; but he finds Merlin standing by his bed, and everything is alright after all.

"I, uh..." Merlin says, the look on his face something between a goofy smile and blind panic. It's an odd combination. "I had to do some physician-things. With Gaius."

He says the last bit with relief. So he expects Gaius to cover for him. Arthur doesn't push it. He knows by now that Merlin is a stubborn liar, if not a skilled one.

"I needed you here, Merlin," he snaps back instead, and glances up at the pale face above him. Merlin looks tired, and though he didn't mean to, he softens his tone when he adds: "Tell me you're not leaving again."

Merlin looks worried for another moment, and then, very suddenly, a smile spreads over his face; and as cheesy as it is, it's like the sun is rising.

"I won't," he says, with more feeling and reassurance than is warranted, surely he didn't sound that worried? "I promise."

And he finds that that's good enough: he has no idea what else Merlin is hiding now; but he has faith enough to be able to trust him in spite of the secrets.