Hrothgar is pleased by Beowulf's boasting and glad he's got this guy on his side.
Enter Hrothgar's wife, Queen Wealhtheow. She salutes the warriors and moves among them, offering them a goblet from which to drink, and she thanks Beowulf for coming.
Beowulf boasts once more that he's going to deliver the Spear-Danes from Grendel. Wealhtheow is pleased with his declaration and goes to sit by her husband.
The banquet continues; everyone laughs and talks and tells stories.
After sunset, King Hrothgar leaves to go to sleep, giving Heorot Hall over to Beowulf's keeping. This is the first time he's ever let anyone be in charge of Heorot except himself.
Hrothgar and Wealhtheow leave and go to bed.
Beowulf trusts himself to God, removing all his armor and putting his weapons aside. Since Grendel fights without weapons, he's going to fight Grendel with his bare hands.
Beowulf and the Geats lie down and go to sleep in Heorot Hall, resting and waiting for Grendel's inevitable attack. They all expect to die, but the narrator tells us that God is planning a victory for them.
Right on cue, Grendel comes lumbering in off the moors to attack the hall. He's drawn back to it again and again, even though it's defended more fiercely than anything else he's ever attacked.
Enraged, Grendel tears the door off the hall, revealing the sleeping Geats. He feels a demonic glee as he imagines murdering them.
Grendel grabs one of the Geat warriors and mauls him, drinking his blood and tearing lumps off him with his teeth.
Grendel raises his arm to attack Beowulf, but Beowulf grabs his arm with the strongest grip Grendel has ever felt. Grendel begins to panic, because he's never met someone stronger than he is.
Beowulf leaps to his feet and wrestles with Grendel, crashing into the furniture and sides of the building. More of the sturdy hall is wrecked than anyone could have thought possible.
Overpowered by Beowulf, Grendel lets loose an unearthly, demonic howl.
Beowulf's men try to help him by striking at Grendel with their swords – but what they don't know is that Grendel can't be harmed by any blade on earth.
Grendel and Beowulf remain locked in combat. Grendel's shoulder begins to tear, and eventually his arm comes off entirely. Grendel flees, mortally wounded.
Beowulf has won! He's fulfilled his boast and saved the Danes from the marauding demon. He even has Grendel's severed arm to prove it.
In the morning, warriors and leaders gather to celebrate Grendel's death. The warriors track Grendel, following the trail of blood he left behind, to make sure he's actually dead…and he is. He jumped into the marsh and drowned there and, the narrator tells us, his soul went to hell.
Everyone rides away again, happy and satisfied, praising Beowulf. In Beowulf's honor, Hrothgar's minstrel sings a well-known song about Sigemund the dragon-slayer, applying some parts of the song to Beowulf's own deeds.