It starts with a promise, such an innocuous thing between friends. Morgana's dreams have been getting steadily worse for months so Arthur isn't hugely surprised when, on rising early one morning to go hunting, he meets her in the corridors all dishevelled and distracted. Her eyes seem a little wild but when she spots him they gain an intent sort of focus. Over time he has grown used to the helpful hints and terrible truths that leak out of the dreams that haunt her sleep. The four of them never speak of the subject but Arthur is certain she has the sight and that it is a curse she never asked for. He expects to have to sift through babbling and nonsense to find the useful truth from her words — or more accurately to rant about it to Merlin who'll seize on the important part of it and make use of it at some vital moment — but she is unusually clear about this one. She makes him promise that, no matter what happens, he'll make sure no harm comes to Gwen, that he'll protect her and keep her safe. It baffles him, as if he wouldn't protect any of them, but he promises anyway as it seems to bring Morgana comfort. Less than a month later Morgana is gone in a whirl of carnage and magic. His father is beside himself with rage, cursing her name and casting suspicion and aspersions on all sides. It takes a lot of persuasion but he eventually convinces his father that it is best to assign Gwen to be Gaius's assistant, that if there is anything to be suspicious of then Gaius is best placed to spot it. Only when he has succeeded does Arthur allow himself to acknowledge that he was arguing for Gwen's life not just her job. He has no words to comfort her but there's something in her voice as she thanks him that makes him think his actions help her more.
The day that Merlin leaves, he extracts a promise from Gwen that she hasn't the faintest idea how to keep. Over the long months since Morgana's departure the three of them have grown increasingly close. With Uther increasingly erratic and dangerous powers threatening Camelot they have no one else to lean on or trust. She carries Merlin's secret as she once carried Morgana's, with love and in fear of the future. She returns to Gaius' chambers with supplies for his journey, to find Arthur already there and mid argument with Merlin. The sight is so familiar it almost breaks her heart, but time is short and Merlin needs to leave and fast. She would do most anything to have him stay and be safe but in the absence of that she would have him gone and safe. She closes the door firmly behind her, drawing their attention to her as she places the supplies on the workbench. Arthur opens his mouth to begin the argument again and something in her snaps.
"Arthur," she says voice rough with unshed tears and frustration. He subsides with only the mildest of mutinous looks. Merlin begins to laugh quietly to himself, an edge of hysteria bleeding into it as Arthur turns to glare at him. In response Merlin swings his hand around, choking out a few words between the laughter, a few books fly from the shelves into his bag, his supplies packing themselves.
He shrugs at her with that same desperate grief she remembers from Morgana's departure, "not a lot of point in hiding now, is there? Anyway, thank you for the supplies Gwen, but you should go. Both of you, if anyone catches you here with me, consorting with a sorcerer…"
"And I'm just supposed to let you go, to accept that my father's crusade against magic must continue into another generation. That I am to allow him to drive everyone that I care for from Camelot? What's the point of being Prince of Camelot, of all my training as a knight if I cannot even protect my own friends? First Morgana, now you Merlin, what next Guinevere?"
"I have no magic, my lord," she whispers. Gwen has seen the power that Morgana could wield, her skill with sword and still she had fled Uther's wrath. Merlin's power has defeated terrible monsters and powerful sorcerers, if not even he dare defy Uther's rage than what hope has she of being safe here.
"The irony of course," says Gaius' quiet voice from the doorway, "is that Merlin's destiny is supposed to be to protect you Arthur. All the good he has done, even if your father knew it wouldn't change a thing." There is a quiet, resigned sort of despair to his voice, and Gwen wonders how it feels to live through this over and over. She wonders how Gaius has managed not to murder Uther in his sleep long ago. How he has survived so close to the flame for so long. He draws Merlin in for a brief hug, hushing Merlin's apologies. "Go. Be safe. Seek out Morgana, if she has not entirely fallen to the dark you may yet be able to do some good."
Gwen pulls Merlin to her to share a hug of her own, Arthur hovers a few feet away moving awkwardly. Until Merlin looses one of his arms to extend it towards Arthur and unthinkingly she mirrors his gesture, they are rewarded with an armful of prince. They cling together for a brief desperate moment before Merlin untangles himself and pulls himself together enough to speak.
"Just, take care of each other alright?" he glances at Gwen and there's the ghost of a smile on his face, "keep this one in line won't you?"
She laughs at that because it's either that or cry and she feels Arthur take her hand as he joins her in agreeing.
The following morning when Uther calls Arthur in front of him, Gwen accompanies him, their hands still joined.
"I promised I would protect her, how else am I to protect her?" he asks eyes and voice as cold as ice.
"Protect her? From what? From who?" Uther laughs.
She meets his eyes unflinching. Perhaps she has lost too many people, to death, to exile, to this man, but she doesn't fear him anymore. She will not lose Arthur. Her voice doesn't even shake when she speaks. "From you."
Camelot is a very different place to the one Lancelot left all those years before. There is a cloud over the kingdom, no less heavy than the one that hung there in the last days of Uther's reign if his new fellow knights speak truly. Neighbouring kingdoms are clearly just waiting for Arthur to slip up before attacking and Arthur himself has other enemies to contend with. Arthur does not share his father's blind abhorrence of magic but too many people look at him and see only his father. There is a distance about the King and Queen when Lancelot first arrives at court. He can't quite place what it is until he is alone with them, when the warmth with which they greet him as they take it in turns to hug him in welcome tells him more than any words. They are not purposefully holding themselves apart from the rest of the court, the distance is merely the space where Merlin and Morgana should be but are not. Beloved confidants-in-exile that they cannot call home. They lean on each other a great deal but the strain is beginning to show, they need another to diffuse the tension. Lancelot is glad to take that strain, revelling in being both their general and their confidant.
The first time is after an attack on the castle. The knights are beginning to flag, he can only rally them so far, and they need their king. He finds Arthur in one of the stairwells, fighting back to back with Gwen. He remembers the days he spent fighting at Merlin's side as he tried to persuade the Druids and others who had aligned themselves with Mordred that now Uther was dead there was no need to fight Camelot, that Arthur was not his father. The relief when Morgana had arrived, and declared herself his ally, sometimes he wonders if he would have answered the summons if he hadn't been able to see the tide turning. Mostly he remembers the promise they'd both extracted from him, to keep Gwen and Arthur safe. Standing in the doorway above them, as they fight together a seamless unit born of years of practice, he feels the low rumble of regret and envy resolve itself into a kind of fierce protective love. They look quite, quite beautiful together. Gwen looks up at that moment and smiles at the sight of him, and he cannot help but join the fray. Enemy defeated for the moment he gives himself a moment to enjoy the affectionate squeeze they each bestow on him before delivering his news. Arthur looks torn for a moment, before Gwen nods and sends him to the men, claiming Lancelot's assistance for herself. Arthur kisses her fiercely and orders them both to stay safe. Together they hold the tower, they do not move quite as seamlessly as she and Arthur do, but they find their rhythm and make a good team. When evening comes and the enemy is defeated, they find Arthur and he greets Gwen with a kiss and Lancelot with a celebratory slap on the back. They stay up late talking and drinking, until Lancelot is unsurprised to find himself being led to bed by the pair of them. In his memory the night is a blur of skin and laughter and adrenaline, which is a shame because he wants to remember every second to keep him warm on cold nights. He doesn't expect it to happen again.
It happens again. At first irregularly, often in those first months, he will find himself tumbling into bed with one or other of them while they are separated. With Arthur it seems simplest, adrenaline and hormones, skin and sensation, after a few too many celebratory drinks on the battlefield far from home. He knows how this goes, any port in a storm as they say. Gwen is more complicated. He loved her for so long, promised himself that he would not allow himself to come between her and Arthur, but she is so very beautiful and so very persuasive. Sometimes her muffled cries are for Arthur others for Morgana, for those latter days he keeps his hair longer than practical and uses only fingers and tongue to give her pleasure. Mostly though, when he shares her bed, it is his name that falls from her lips. He worries a little, until the day Gwen walks in on he and Arthur in bed and Arthur simply offers her his hand. She takes it with a smile and offers her other hand to Lancelot. He takes it and from then on, in those rare times when it just two of them it no longer feels like cheating. He is uncertain what he has done to earn this delight, but he works hard to ensure he deserves it.
Some times are easier than others. They are close; this is common knowledge. The knights are well aware that Lancelot can get away with comments that the King would tolerate from no other. Well none that still resides in Camelot. Some days are hard. When duty takes Lancelot far from Camelot, especially when he must depart suddenly without time for private goodbyes, when even the courtesy of a kiss to Gwen's hand is too much to ask for. When they have guests that mean he must sleep in his own chambers, he misses the warmth of their shared bed. Rumours may occasionally surface that he is sharing one or other of their beds and he gladly spars with many of the knights to protect their and his own honour, but they never come close to the truth and he is glad of it. They have to be so very careful. He watches the easy affection that the King and Queen share and he envies them that. He cannot kiss either of them in public, cannot share his joy in victory or despair in defeat with either of them until they are safely behind closed doors. He never mentions the matter to Gwen or Arthur but they must see and speak of it between themselves, for he finds they have developed a sort of code. A pattern of platonic but comforting gestures, that seems innocuous but also marks him as theirs. He feels it in the way Arthur slings his arm round Lancelot's shoulder after a sparring match or in the quick squeeze Gwen give his arm when he offers her it to escort her in to dinner. Slowly he comes to believe that they are his, every bit as much as he is theirs. He has never doubted that he would die to protect either of them in an instant, but it comes as a shock to discover they would do the same.