This is the first of a two parter. There is a quote that says "Being loved deeply by someone gives you strength; loving someone deeply gives you courage." Obviously here it's a best friend/brother kind of love, but I feel it still applies.

"He won't speak, Pendragon."

Arthur said nothing, but continued glaring at his captor.

"He refuses to betray you, your majesty," the man mocked, sneering. "So when he dies, that will be on you. I wonder what makes him so loyal to a man who can't even save him."

With a surge of adrenalin, Arthur pulled at the ropes tying him back. He managed to get one hand free, but he wasn't entirely sure what to do next.

But Merlin was counting on him. And when the man believed in him that strongly, cared that deeply, Arthur couldn't let him down.