The episode begins with Sam and Jon standing guard on top of the wall at night. Sam is asking Jon about Ygritte, but Jon is reluctant. Jon asks if Sam would have broken his vows with Gilley if he had the chance. Sam note that there is a loophole about non-reproductive sexual activity. Jon ties to describe his time with Ygritte, but barely has any words for it. Jon takes the next watch and sends Sam to get some sleep.
Tormund, Ygritte and the other Wildlings in his party are sitting around a fire. Tormund is telling a tale of how he had sex with a bear, but Ygritte doesn’t want to hear it. She is fletching arrows for the Night’s Watch. The Magnar of Thenn questions her real willingness to kill. Ygritte proclaims Jon Snow as her’s to kill and says she’ll put an arrow in anyone else who tries.
Sam is in the library when he is joined by Maester Aemon. Sam says he’s reading about the Wildlings, but Aemon says the source is not reliable. Aemon tells Sam the same thing he told Jon: “love is the death of duty.” Though Sam tries to hide it, Aemon insists that Sam is in love with Gilley. Aemon recounts the girl he was with once, back when he was still a king-in-waiting. He then sends Sam to bed.
Sam leaves the library and hears Gilley at the gate. He convinces Pip to open the gate to let her in, despite orders not to. He pledges that, from now on, wherever Gilley goes he will follow. Horns blow announcing Wildlings at the wall.
At Tormund’s camp, their warg awakens to tell them that it is time.
Jon Snow looks out over the wall at the massive army Mance Rayder has brought with him, silhouetted in flame. The Night’s Watch begins mounting their defenses, including barrels of oil. He runs into Alliser Thorne, who admits they should have sealed the gate when they had a chance, as Jon said. Alliser says a leader can’t second guess himself, but that this won’t be the end as long as everyone does their job.
Sam brings Gilley and her child down to the food pantry to hide. Gilley doesn’t want him to leave. Sam says he has to go defend the wall because keeping a promise is what men do, then kisses Gilley. He promises her he won’t die, then leaves.
Pip is setting up his arrows in oil to burn, but his nerves is getting the better of him. Sam tries to reassure him. He tells him how he felt like nothing at all when he killed the White Walker, and when you’re nothing there’s no reason to be afraid. But he’s not nothing anymore.
Ygritte scouts the ahead and reports back to the raiding party. They ready to attack Castle Black. Mance Rayder’s army marches forward, with giants riding mammoths.
Alliser is readying the men on top of the wall to fire when he his alerted to Tormund’s party. Arrows begin to fly as Tormund’s party reaches the southern gate. Alliser heads to the southern gate, leaving the wall under Janos Slynt’s command.
The Night’s Watch at the southern gate try dropping stones on the raiding party, but the party just begins climbing the walls. Alliser rallies his men, asking them if they want to fill the belly of a Thenn. The Wildlings get inside and begin to fight the Night’s Watch. Tormund reaches the walkway where Pip and Sam were. The Watch retreats from that position.
The giants begin moving to ram the gate. Janos begins rambling about how giants don’t exist. Grenn lies to him about being summoned by Alliser to get him out of the way. Jon hangs some archers over the side of the wall so they can fire straight down at the climbers. A giant fires up the wall with an arrow, sending a Watch brother launching off the side of the Wall.
The Thenn are slaughtering as they go. Ygritte continues to kill with her arrows. Janos makes it back down the wall. He goes and hides in the pantry where Gilley is.
Pip kills a Wildling, but then Ygritte puts an arrow in his neck. Sam tries to comfort him.
Jon ends barrels of oil down to the bottom of the wall. A giants latches his mammoth to the gate so the beast can pull it out. Jon realizes the outer gate won’t hold, so he sends Grenn with five men to hold the inner gate.
Allis and Tormund run into each other nad begin fighting. Alliser gets knocked off the walkway and is pulled away as he screams for the Watch to hold the gate.
Sam makes a run and is charged at by a Thenn. Sam uses a crossbow to put a bolt in his face. Grenn runs by. Sam says they need more men but Grenn just tells him to talk to Jon. Sam has to convince the boy from the town Tormund raided to raise the lift, then tells him to find a weapon and fight.
Jon send an explosive barrel over the wall to set the mammoth on fire. It runs and the watch kills one giant with an arrow, but the other giant is lifting the gate himself. Another barrel explodes while still on the wall, sending several Watchmen to their death. Sam reaches Jon and asks for help. Jon leaves Ed in charge and follows Sam.
Grenn’s reach the gate as the giant makes its way in and charges the inner gate. The men recite the oath as he comes.
Jon tells Sam he doesn’t want him in the fight. Sam protests, but Jon hands him a key and says he needs “him” more than Sam. Sam uses the key to let Ghost loose, and the dire wolf immediately mauls a Thenn. The Magnar comes at Jon and they fight. Ygritte sees them. The Magnar has the upper hand until Jon gets his hands on a smith’s hammer and puts it in his skull. He turns to see Ygritte with and arrow drawn at him. He smiles and she hesitate, but the boy Sam encouraged to fight puts an arrow in her chest. She collapses in Jon’s arm and tells Jon they should have stayed in that cave. He says they’ll go back there, but she says “you know nothing, Jon Snow” and dies in his arms.
On the wall, Ed orders them to drop the wall and releases a chain cause a layer of the wall to crumble with the Wildlings still climbing.
Tormund refuses to surrender, but Jon puts a bolt in him and they take him captive. Tormund says they should have thrown Jon from the top of the wall, and Jon agrees.
The next day Jon is less that ecstatic about their victory. Mance still has a massive army. The Watch can never hope to win. Jon decides to go find Mance himself, without any orders. Sam tells him he’ll never get close, but he doesn’t have another plan.
Jon and Sam walk into the tunnel to find Grenn, his five men, and the giant all dead. Jon tells Sam to burn the bodies. Jon gives Longclaw to Sam in case he doesn’t come back and then walks outside.