Game of Thrones - Season 2, Episode 9 Synopsis
 

Episode 2-9
Title: "Blackwater"
Directed by Neil Marshall
Written by George R. R. Martin
Original Air Date: May 27, 2012

Stannis Baratheon's fleet assaults King's Landing in the Battle of Blackwater Bay. Leading the defense, Tyrion Lannister destroys many of the attacking craft with an exploding ship full of wildfire, and is forced to lead a counterattack as King Joffrey and his bodyguard Sandor Clegane each desert the battlefield. Stannis' forces make it inside the castle, but Tyrion leads his men behind the Baratheon forces via underground tunnels and attacks. Meanwhile, Queen Regent Cersei, holed up in the fortress with Sansa Stark and the other ladies of the court, succumbs to wine and despondency as she believes the battle lost. In the nick of time, as she is about to poison her son Tommen, Tywin Lannister's forces, joined by Loras Tyrell, the lover of Renly Baratheon, arrive to dispatch the attackers.

Source: http://en.wikipedia.org/wiki/Game_of_Thrones_(season_2)