This is the episode that first showed viewers that Game of Thrones had no qualms about killing off lead characters who everyone likes. In the penultimate episode of season one, King Joffrey, in typical human-scum fashion, almost makes everyone think he's going to show Ned Stark mercy — and then sentences him to death, right in front of his daughters.
That's what most people remember about this episode. However, there's a lot more going on that makes this episode so interesting and sets up a lot of later action. Daenerys puts her trust in Mirri Maz Duur to heal her husband's wounds (which as we now know goes very wrong). Catelyn Stark and Walder Frey strike up their fateful deal: the Freys will join the Starks in their war against the Lannisters, in exchange for Robb marrying one of Lord Frey's daughters. Robb also wins his first major battle against the Lannisters and captures freaking Jaime Lannister himself. And then there's the minor detail that Maester Aemon at Castle Black is actually Aemon Targaryen. No big deal.
