With their wedding hours away, Tyrion Lannister (Peter Dinklage) visits Sansa Stark (Sophie Turner) to ease her apprehension at the prospect of being his wife. In the Sept of Baelor, Queen Cersei Lannister (Lena Headey) threatens Margaery Tyrell (Natalie Dormer) with the story of House Reyne, former Lannister vassals who her father Tywin (Charles Dance) exterminated when they rebelled against their liege lord. After arriving at the Sept, Sansa is walked down the aisle by King Joffrey Baratheon (Jack Gleeson). In an effort to embarrass Tyrion, Joffrey departs with the stepstool Tyrion was to use to cloak Sansa with the Lannister colors. After some snickering from the crowd, Tyrion gets Sansa to kneel, and they are married.
At their wedding feast, Tyrion gets very drunk, irritating both Sansa and Tywin, who counsels his son to stop drinking and begin trying to conceive a child with his new wife. Joffrey, after threatening to rape Sansa, calls for the traditional bedding ceremony to begin, but his plan is thwarted when Tyrion threatens to castrate an outraged Joffrey. Tywin defuses the situation, and Tyrion is able to avoid punishment, using his intoxication as an excuse. Tyrion departs the feast with Sansa, and though Tywin has ordered Tyrion to consummate his marriage, he tells Sansa he will not share her bed until she wants him to. Sansa asks what Tyrion will do if that never happens, and Tyrion jokes by saying a phrase from the Night's Watch vow, "And so my watch begins", meaning that he is resigned to never having sex again within their marriage.
Melisandre (Carice van Houten) returns to Dragonstone with Gendry (Joe Dempsie). She then takes him to see King Stannis Baratheon (Stephen Dillane), who recognizes Gendry as one of Robert's bastards. When Gendry is taken to his chamber, Stannis and Melisandre discuss what they intend to do with him.
In the dungeons, Davos Seaworth (Liam Cunningham) continues to learn to read. Stannis visits him to discuss Melisandre's plan to sacrifice Gendry. Davos objects to the plan, seeing Gendry as a nephew to Stannis, but Stannis remains resolved. He then makes Davos swear to never try to kill Melisandre again, and frees him.
Later, Melisandre visits Gendry, and after a short discussion, she disrobes him and they begin to have sex. Melisandre, who has earlier stated that there is "power" in Gendry's kingly blood, binds Gendry's hands and legs and lays three leeches on him to draw his blood. Afterward, Stannis arrives and ritually burns the leeches, speaking the names of the usurpers to his throne: Robb Stark, Balon Greyjoy, and Joffrey Baratheon.
Arya (Maisie Williams) tries to kill Sandor "the Hound" Clegane (Rory McCann) while he is sleeping, but he is revealed to be awake, and thwarts her attempt on his life. They depart their camp and head for the Twins, where Clegane intends to ransom Arya to her brother Robb.
Ser Jorah Mormont (Iain Glen) tells Daenerys Targaryen (Emilia Clarke) that Yunkai has employed a mercenary group called the Second Sons, which is led by a man named Mero (Mark Killeen). Daenerys soon meets with Mero, his co-captain Prendahl na Ghezn (Ramon Tikaram) and his lieutenant Daario Naharis (Ed Skrein). She attempts to bribe Mero to renege on his deal with Yunkai and fight for her, and gives him two days to make a decision. In the Second Sons' camp, the three leaders plot to kill Daenerys that night, with one of them sneaking into her camp. By random draw, Daario is selected to carry out their plot.
After nightfall, Daario enters Daenerys' camp, disguised as an Unsullied soldier. He enters her tent and shows her and Missandei (Nathalie Emmanuel) the severed heads of Mero and Prendahl, admitting that he is smitten by Daenerys and killed his superiors after disagreeing with the plot to kill her. He then kneels and pledges the Second Sons, as well as himself, to her cause.
Samwell Tarly (John Bradley) and Gilly (Hannah Murray) continue their journey to the Wall. They stop at an abandoned hut for the night and discuss a name for her son. When they hear a murder of crows cawing nearby, Sam leaves the hut to investigate. Soon after, he is attacked by a White Walker, which shatters Sam's sword with a single touch and tosses him aside. The Walker moves towards Gilly, intent on taking her son, but Sam stabs it with his dragonglass dagger, causing it to disintegrate. Sam and Gilly then flee into the night.
"Second Sons" was written by the show creators and executive producers David Benioff and D. B. Weiss, based on material from George R. R. Martin's novel A Storm of Swords. The episode adapts parts of the book's chapters 19, 29, 37, 43, 47 and 48 (Samwell I, Sansa III, Davos IV, Daenerys IV, Samwell III and Arya IX).
The episode introduced the mercenary captains in service of Yunkai: Mark Killeen was cast as Mero (known as the Titan's Bastard), Ed Skrein the recurring role of Daario Naharis, and Ramon Tikaram the part of Prendahl na Ghezn. Tikaram is mistakenly credited as "Ramon Tikrum" in the closing credits.
Most of the scenes of the episode were shot in the Belfast studios of The Paint Hall, including the wedding of Tyrion and Sansa that was filmed at the huge semicircular set of the Great Sept of Baelor in mid September 2012. For this scene, a few hundred extras were recruited.
The episode received 5.1 million viewers, an increase from the previous week, with an 18-49 demographic of 2.6. In the United Kingdom, the episode was seen by 0.907 million viewers on Sky Atlantic, being the channel's highest-rated broadcast that week.
"Second Sons" received critical acclaim. Review aggregator Rotten Tomatoes surveyed 20 reviews of the episode and judged 100% of them to be positive. The website's critical consensus reads, " 'Second Sons' shines through efficient storytelling -- and a comparatively low number of storylines to keep track of this week." Writing for IGN, Matt Fowler rated the episode a 9.0/10, and wrote "This week's well-crafted and wonderfully acted Game of Thrones gave us a cold wedding, a hot bath and a blood-letting." He especially praised the scenes between Sansa and Tyrion and between Ser Davos and Stannis. David Sims and Todd VanDerWerff, both writing for The A.V. Club, gave the episode "B" ratings. Sims was frustrated by the episode's meandering pace, but praised the end of the episode, with Sam killing the white walker, as "the most crucial, fascinating, electric moment of the night". VanDerWerff praised the use of nudity in the episode, writing "...I actually think Game Of Thrones has gotten quite a bit better at utilizing nudity and sex in the midst of everything else as a method of telling its story. It’s come a long way from the 'sexposition' days of season one, when it sometimes seemed like the series would toss some breasts into the background of a scene just in case we got bored of hearing somebody talk at length."
Due to his nomination, Peter Dinklage submitted this episode for consideration for the Primetime Emmy Award for Outstanding Supporting Actor in a Drama Series for the 65th Primetime Emmy Awards.
At the 65th Primetime Creative Arts Emmy Awards, the episode was nominated for Outstanding Hairstyling for a Single-Camera Series.