Arthur's first clue that something isn't right is the way Merlin walks into his room and smiles at him.
The fire and the screaming villagers are the second clue.
"Merlin," Arthur starts.
"Arthur," Merlin answers.
He's not quite smiling, but Arthur can tell Merlin's planning something. It's happened more than once, especially now that Arthur's king of Camelot. He's found that the more danger there is, the more Merlin tries to distract him and keep him inside. He doesn't do it outright, won't ever say it to Arthur's face, but Arthur can tell. Merlin will come to Arthur's rooms , ask him mundane kingdom questions and look at him just as Morgause's army attacks Camelot's borders. Or Merlin will suggest that Arthur go on a hunt right before Cendred's army attacks and Arthur's never been good at saying no to Merlin.
It's not that bad things happen per se, because the knights are good at what they do. But, Arthur is tired of listening to Gwaine recount stories of how he single-handedly took down three men. All Arthur can do is nod along and tell them how he single-handedly took down a boar. Somehow, Arthur's stories don't feel as impressive then.
Merlin looks at him now as Arthur scans the room. He's already put on his armour. The only thing he needs is his--
"Merlin," Arthur says, breathing hard through his nose. "Where's my sword?"
Merlin turns wide, blue eyes on him. "Your what?"
Arthur tries, he really does try, to keep his temper. He can feel the pulsing headache beginning to the right of his skull and he'd rather end this discussion before things get out of hand.
"My sword, Merlin. You know, the sharp pointy thing that I use to defend Camelot. That sword."
"Oh," Merlin says as though this is new to him, as though Arthur doesn't ask him to polish the damn thing, every day. "I put it away."
Arthur stares at him. "You, put it away?"
Merlin shrugs, "I figured since you're busy with the kingdom affairs, sire, you wouldn't be needing it any time soon."
"Busy," Arthur asks and he's not sure whether to be angry or concerned that Merlin seems to have lost all reason. "With kingdom affairs? Merlin, in case you hadn't noticed, this," here Arthur pauses to wave at the window through which the noise of falling homes can clearly be heard. "This is a kingdom affair."
"I get that, sire," Merlin nods stepping away from the door and coming towards Arthur. "But, you have other duties to attend to. Duties for the greater good of the kingdom."
"Greater good," Arthur says narrowing his eyes. "Greater good of the kingdom. Are you aware that if I don't go out to defend my kingdom there will be no need for duties that concern the greater good?"
Merlin, Arthur is sure, is aware of this. But, he's still standing there looking for all the world like they're discussing dinner options. Arthur can hear the battle cry from Gwaine and he's itching to pick up his sword and join the knights. He can't really see what they're fighting, there's fire, could be a dragon.
"Merlin," Arthur growls.
"Morgana has it."
"Morgana," Arthur roars.
It takes about a second for Morgana to open the door and Arthur wouldn't be surprised to know that she'd been listening outside. "Yes," she asks, blinking at him.
"Where's my sword?"
Arthur doesn't miss the look Morgana exchanges with Merlin. He turns and glares at Merlin who just smiles back at him as though Arthur is the most amusing thing he's seen in a while.
"I don't know why you'd need that thing."
"Oh, all right," she says. "Gwen has it."
And that is how Gwen, Gwaine, Percival, that stable boy that Arthur has seen with Morgana's chamber maid, plus said chambermaid end up in Arthur's room.
"So," Arthur says once they've gone through it all again and Arthur's resigned himself to not being in this battle. "I'm to assume that no one knows where my sword is?"
Merlin just laughs.