17 AGOT Eddard III: Damages

Arya is brought before the king for judgment and the queen calls for Lady's pelt as a trophy. Lord Stark kills Lady, himself, to deny the queen her trophy. But the Hound has ridden down Mycah, his body cut nearly in two.

Ned's outrage is central in this chapter about the impositions of royalty. Though it is subtext, the shock of Mycah's "execution" points out that the royal family would presume to slay an innocent child, something a healthy society would never conscience.

The chapter raises the question of what a good royal family is like. Afterall, what are royals for when not imposing and playing superior? We see Robert imposing on Darry. In the context of tensions from Robert's Rebellion, his license seems rude. Darry lost his three older brothers, supporting Rhaegar at the nearby ruby ford, yet Robert takes the high seat as an uninvited guest. Within this setting,

The chapter ends with a gut punch: the relief the body is not Nymeria seems to indict us when it is Mycah. The double take points out that affections and disagreements, all presumably biased, prevent any ruler from being objective.

Robert's state, increasingly, seems caused by Cersei's demands upon him. Seen indoors, it's clearer the Lannisters have him surrounded by soldiers.

Lady's death seems especially tragic in that it ruins the sense that the direwolves could protect the Stark children. Who can protect against the king's justice?

References

When Jaime revisits Darry in AFFC, he tells Ser Ilyn Payne:

My sister wanted the girl to lose a hand. Robert told her she was cruel and mad. They fought for half the night... well, Cersei fought, and Robert drank. Past midnight, the queen summoned me inside. The king was passed out snoring on the Myrish carpet. I asked my sister if she wanted me to carry him to bed. She told me I should carry her to bed, and shrugged out of her robe. I took her on Raymun Darry's bed after stepping over Robert... As I was fucking her, Cersei cried 'I want'. I thought that she meant me, but it was the Stark girl that she wanted, maimed or dead. It was only by chance that Stark's own men found the girl before me. If I had come on her first...

Arya's disappearance may reflect Lyanna's.

There's a major intersection between Sansa's arc about Lady's death, the unfairness of being punished for your brother's crime, and Eddard's regarding mercy.