"Do you trust me?" Merlin asked so softly Arthur thought he had heard wrong until Tristan looked up at Merlin. The desperate man clutching to Isolde stared at Merlin for a moment, hope flaring when it shouldn't have. He nodded once slowly before whispering back "Yes."
With that, Merlin knelt down next to him, "Give her to me." Tristan held her tighter, and she squeezed him back, savoring the last few seconds in his arms. Then, all too soon for both of them, she was gone, now in another man's arms. Merlin made sure she was comfortable, glancing up at Arthur's confused, tear-filled eyes during the process.
"Merlin, what the-" Arthur started, but Merlin interrupted him.
"Shut up, Arthur," he said in a much stronger and commanding tone Arthur had ever heard from Merlin. Arthur clapped his mouth shut in response, unused to this side of Merlin. Merlin placed his hand over Isolde's wound and locked eyes with Arthur. He seemed to struggle internally before saying "I'm sorry for lying to you. You have to realize why though." With that, he looked down at his hand, now dripping blood.
A cold chill went up Arthur's spine as Merlin started to speak in the language he had learned to associate with magic use. Arthur tensed. There was a still moment where nothing happened. Isolde's gasp broke the silence and right in front of Arthur's eyes, her wound healed itself. Tristan let out a breath himself, laughing with relief. Gwen looked on with a bright smile and joyful tears streaming down her cheeks. Merlin cracked a smile as well.
Arthur couldn't bring himself to celebrate though. No, celebration was the last thing on the king's mind. His heart was pounding in his ears and he felt faint. "You have magic?" he asked tensely.
Instantly the warm, happy feeling that had started to fill the air vanished. Without looking at Arthur, Merlin slide Isolde off of his lap and stood up. Arthur took a step back as the other man approached him. Sharp, stinging betrayal threatened to choke him. How could Merlin, the man he trusted above all others and quite possibly cared for above everyone, lie to him like this? And for how long?
"Arthur, let me explain," Merlin began.
"No." Arthur growled, making Merlin take a step back. He winced at the absolute raw hurt, sadness, and confusion in his voice. Tears pricked the corners of Merlin's eyes. He looked down, not wanting to see the expression of hate on Arthur's face. His worst fear had come true. Arthur was repulsed by him. That hurt more than Merlin could have ever imagined.
The king took one decided, albeit slightly shaky, step forward before stopping and just staring at Merlin. Time seemed to stop; no one moved nor said anything. Everything seemed to be holding its breath, just waiting. The spell ended when Sir Leon, Sir Percival, and Sir Gwaine burst through the door, swords drawn and ready to fight. Their surprise at seeing Arthur glaring at Merlin, Tristan and Isolde still on the ground, and Gwen standing awkwardly out of the way was immense. It was greater still when Arthur said "How could you keep this from me?"
"Did we miss something here?" Gwaine asked no one in particular. Percival slammed Gwaine across the back of the head. "Ow!" Gwaine said, looking at Percival and rubbing the back of his head.
Arthur cleared his throat and turned to face the knights. "Arrest him." Merlin squeezed his eyes shut, tears threatening to spill over.
The knights couldn't help themselves; they laughed. "Who, Merlin?" Sir Leon asked laughingly. The smile slipped from his features at Arthur's firm nod. "Sire?"
"Do it now!" Arthur barked. Leon and Gwaine jumped forward, each one grabbing one of Merlin's arms. They led Merlin across the floor and to the door.
Merlin stopped and turned his head once at the door. He gazed sadly, almost longingly, at the king's back. "Arthur," he murmured. "Please forgive me. I did what I had to. Surely you can understand." With that, Leon and Gwaine swept him from the room.