Note: Mild spoilers for episode 1x10 "The Moment of Truth." Many thanks to Thedoingofit for the prompt and beta.
Will had only wanted a bit of fun.
The other children were all busy or didn't want to play with him, and Will was bored. So he decided to string a thin bit of rope low to the ground behind the barn where he knew some of the older boys would have to pass on their way to tend to the animals. It was meant to be funny. How was he to know that all the milkmaids would be there to see the boys fall in a heap in the mud?
"Get him!"
Over the sound of the other boys' feet squelching in the muddy grass and his own harsh and panting breaths, Will could still hear the girls' laughter. He forced himself to run faster until he finally reached the woods. Quickly he ducked under a low-hanging branch, hoping to throw the others off his trail before venturing deeper into the trees. He thought he'd finally made his escape when a large figure unexpectedly loomed before him.
It was one of the older boys; Peter, the spotty one with the big nose. Will shrank back but the boy grabbed him by the collar of his shirt and pushed him towards his two companions, who immediately held fast to Will's arms.
"You hold him, and I'll hit," Peter said. He smiled nastily at Will. "And then we'll trade places."
Though he struggled, Will couldn't manage to free himself. He flinched away from the punch that was certain come at any moment.
Suddenly there was a loud crack, and a large branch crashed down onto the ground beside them. A second branch fell on the other side, raining splinters of wood on their feet.
Around him the other boys shifted uneasily, glancing up at the branches. But Will stared straight ahead, where a dark-haired boy about his own age stood nearly hidden behind a nearby tree.
His name was Merlin. Will had seen him before in the village, walking and working alongside his mother. He mostly kept to himself, rarely playing with the other children, and some of the other villagers wondered if he was sickly. But now as Will watched Merlin standing there with his hand outstretched and his eyes glowing gold, he saw that he wasn't sickly. He was just… different.
The tree began to vibrate, its leaves rustling wildly overhead and its roots beginning to lift out of the ground. It twitched and shuddered as if it were coming to life.
"Let's go!" Peter cried, and Will found himself dropped unceremoniously onto the ground as the boys pushed past him in their haste to leave. But Will paid no attention to them. Instead he continued to watch Merlin, who was lowering his arm and whose eyes were returning to their normal blue colour. The tree's movements immediately slowed, its roots settling deep in the earth once more.
Merlin grinned, looking quite pleased with himself, but his smile faded as soon as he noticed that Will was watching him.
"How did you do that?" Will demanded as he scrambled to his feet.
"I didn't do anything," Merlin said. His eyes were wide and frightened.
"Yes, you did," Will said. "You dropped those branches. You moved that tree – you almost pulled it out of the ground!" His voice did nothing to hide that was a little envious and very impressed.
"No, I – I don't know how it happened," Merlin insisted, backing away.
Will grabbed Merlin's arm, preventing his escape. "Your eyes turned yellow."
"Please," Merlin said desperately. "It's meant to be a secret. You can't – my mother–"
"I won't tell anyone," Will promised.
Merlin shuffled his feet, looking extremely unhappy. "My mother said that if anyone ever found out, we'd have to leave Ealdor."
"No, you won't," Will said. "Because I'll never tell another person. They'd have to kill me first."
Merlin studied him for a long, troubled moment before he smiled, seemingly reassured by whatever he saw in Will's face. "All right," he said. "I believe you."
"Why did you do it?" Will asked, regarding him curiously.
"Do what?"
"Why did you help me?"
"I saw what happened, and I followed you here," Merlin said. "You didn't mean to hurt them but they wanted to hurt you. So I stopped them."
"What else can you do?"
Merlin shrugged. "I don't know. Lots of things. Sometimes I don't even think about what I'm doing. It just happens." He gave Will a sidelong glance, his expression turning mischievous. "I could find a way to get back at those boys."
Together they crept back to the village. Behind the barn they found Peter and the other boys perched on the fence and boasting to the milkmaids about how they had taught Will a lesson. They were still splattered with mud from their earlier fall.
"I don't think they're muddy enough," Merlin whispered. His eyes flashed gold and suddenly there was a loud, splintering crack as the fence collapsed beneath the boys, sending them face-first into the mud, much to the amusement of the girls.
Laughing, Will and Merlin made their escape. When they reached his home, Will hesitated in the doorway
"Merlin?"
"Yeah?"
"Thanks," Will said. "For everything."
Merlin grinned. "You too."
Will grinned back, and went in for supper.