Wildlings on the south side of Castle Black await their signal from the north. The group is impatient, especially Ygritte, who sneers at Tormund's lighthearted campfire story. Her focus is on the upcoming battle, and shooting as many crows as possible. Styr questions Ygritte's commitment to killing - especially when it comes to her former lover. Ygritte assures the Thenn that she will be the one to take him out: "Jon Snow is mine."
Samwell Tarly and Jon Snow stand watch atop the Wall. Sam probes Jon for details about his relationship with Ygritte, reasoning that Jon's stories may be the closest he ever comes to intimacy. Nothing happened with Gilly, Sam shares, but even if it had, there's nothing in the Night's Watch vows that specifically forbids sex. Jon reflects upon his romance, dismayed it ended in a hail of arrows. Both men lament that more violence is inevitable, as Mance's army bears down on the Wall.
Maester Aemon finds Samwell Tarly reading by candlelight in the library. Realizing that Sam has abandoned his post to research Gilly's predicament, Aemon reiterates what he once told Jon: "Love is the death of duty."
En route to his quarters, Sam is shocked to see Gilly and her baby at the gate, begging for entrance. Sam orders Pyp to stand aside and swears he will never leave Gilly again. Their reunion is cut short by two horn blasts. The men begin preparing for attack; Jon climbs to an outlook and sees, as promised, the greatest fire the North has ever seen.
Sam ushers Gilly to the Castle Black larder to keep her out of the fray. She's distraught at the idea of Sam joining the battle, but he explains that he must do his duty. "That's what men do," he adds, and the two share their first kiss. Before leaving, he promises Gilly he will survive. Later, as Sam tries to soothe Pyp's frayed nerves, Sam confesses that he wasn't afraid when he fought the White Walker. Things are different now, Sam realizes, because he has much more to live for.
Alliser Thorne oversees the top of the Wall as the men ready their defenses. The acting commander concedes to Jon that he should have sealed off the tunnels, but leadership means making the hard choices. Thorne informs Jon they'll work together against the enemy tonight, but when it's over, they'll go on hating each other.
Hundreds of thousands of wildings, including mammoths and giants, charge the Wall. As they approach, a horn announces the attack on the southern gate. Thorne tends to the second front, leaving Janos Slynt in charge at the Wall. Slynt freezes in panic, cowering in a corner until Grenn comes up with a story to send him below. Jon takes command, supervising the archers to send flaming arrows at the climbers on the Wall.
On the ground, giants affix a series of spikes to the gate, attaching the other ends to the harness of a mammoth. Jon sends Grenn down, commanding him to hold the gate at any cost. From atop the Wall, crows drop buckets of oil, which implode on the giants and mammoth, leaving Mag the Mighty to take on Grenn's band of men. As the giant charges them, Grenn leads his brothers in a recitation of their vows and spurs their courage.
Thorne rallies the men of the Watch and the group bravely faces off against the Thenns who have infiltrated the courtyard. Olly looks on in horror as he watches Styr, the man who promised to eat his parents, hack through men left and right. Ygritte shoots an arrow straight through Pyp's neck, and the boy dies in Sam's arms. Tormund takes on Alliser Thorne and seriously wounds him.
Sam realizes more men are needed on his front and he orders Olly to hoist the elevator and grab a weapon. At Sam's behest, Jon leaves Edd in charge and heads to the courtyard. Jon instructs Sam to release Ghost, who jumps right into the fight.
Jon faces off against Styr, and ultimately kills the Thenn with a hammer. He staggers to his feet, and sees Ygritte with an arrow pointed right at his heart. She hesitates for a moment, and is hit from behind by Olly's arrow. Jon rushes towards to her side and cradles Ygritte as she dies.
Under Edd's command, the Night's Watch uses a giant scythe to slice the remaining climbers off the Wall. The battle ends. Refusing to surrender, Tormund is taken hostage. Samwell returns to Gilly in the larder and is startled to find Slynt cowering in a corner.
The next morning, the men assess the carnage. Jon knows that although the crows won the battle, Mance will attack again that evening. With their diminished numbers, they don't stand a chance. Jon decides to treat with Mance, and kill the king beyond the Wall. "It's a bad plan," Jon admits, but it's the only one they have. On the way out, Jon finds the body of Grenn, who died holding the gate. Jon hands Longclaw to Sam for safekeeping, and steps out of Castle Black.