Contains spoilers for this episode and earlier episodes.
Jon and Sam wait on the Wall as the wildling attack approaches. Gilly reaches Castle Black with her baby, and Sam shelters them in the kitchen before returning to the defense. Mance's army advances from the north while Tormund, Ygritte and the Thenns assault the castle from the south. Thorne descends to fight in the courtyard, leaving Slynt in charge above. When Slynt proves unable to command, Grenn tricks him into leaving. Giants and a mammoth attack the outer gate, and Jon sends Grenn's group to hold the inner passage.
Tormund wounds Thorne, and Ygritte kills Pyp while Sam helps him reload his crossbow. Sam brings word that the courtyard is being overrun, prompting Jon to leave Edd in command of the Wall and join the fighting below. Ghost is released, and Jon kills Styr. Ygritte confronts Jon but hesitates when they see each other. Olly shoots her, and she dies in Jon's arms. The defenders swing a huge blade across the Wall to cut down climbers. They capture the wounded Tormund, while Edd's men repel the attack above. By morning, Grenn and his companions are dead beside the giant they stopped in the tunnel. Jon leaves Longclaw with Sam and walks north alone, intending to kill Mance before another assault.