A Dane named Unferth challenges Beowulf by bringing up a swimming contest that Beowulf lost. Jealous of the attention Beowulf is receiving and his bravery, Unferth informs everyone that the Geat, in his arrogance, dared Breca to “a swimming match on the open sea.” It lasted seven nights, in treacherous conditions, but Breca came away the victor. Unferth notes that he doesn’t care if Beowulf has won multiple battles since that loss, there is no way he can beat Grendel.

Beowulf responds by accusing Unferth of being courageous enough to announce his loss only because he is drunk. He seeks to correct Unferth’s account of the swimming match. Beowulf and Breca grew up together and made a habit of challenging each other to contests like the one on the open seas. He claims to have been the stronger swimmer of the two and reveals that both of the men were evenly matched for five nights. He and Breca each wielded a sword as protection against sea creatures and wore armor, which made the swim more difficult. One night, a storm separated them, and the beasts of the open water besieged Beowulf. He was pulled underwater by one creature but used his sword to kill the beast and save himself. Beowulf recounts numerous battles with the “foul things” of the sea, claiming that he always kept pace with the beast attacking him. Even though he lost the race with Breca, Beowulf cleared the sea of dangerous beings that threatened the surrounding communities. 

Beowulf notes that Unferth has not fought in any such contests before accusing him of betraying and killing his “own kith and kin.” He calls out his challenger for not already killing Grendel himself and boasts that the monster will not find him so easy to defeat as the Danes he has dominated thus far. Hrothgar seems to approve of Beowulf’s behavior, and the Danes trust his word. Hrothgar’s queen, Wealhtheow, arrives at the banquet and ceremonially offers a goblet first to her husband and then to other warriors in order of rank. The queen thanks Beowulf for coming to her rescue and answering her prayers. He replies by formally boasting of the “fixed purpose,” his mission in traveling to Hrothgar’s kingdom and insists that he will defeat Grendel or die fighting the beast. Wealhtheow is pleased, and the feast continues, reminiscent of the old days of Heorot before Grendel’s terrorism began. 

Beowulf knows that he must rest to prepare for Grendel’s arrival, recognizing that the beast has had all day to plot and save up his energy for his next strike. When Beowulf leaves the feast, Hrothgar makes him “hall-warden,” for the first time turning over leadership of the hall to another man. He notes that Beowulf will be rewarded handsomely if he achieves his task. The king and queen depart to go to bed, and a lookout has been posted; God is protecting Hrothgar, so Grendel cannot get to him. Beowulf prepares for bed, taking off his armor. He tells his men that he thinks he is “as dangerous any day as Grendel.” Since Grendel will not use weapons, Beowulf will not use them either. He concludes that God will choose the most worthy victor. His men are not expecting to survive the battle, but Beowulf feels confident that he will win the fight. 

Grendel stalks toward the hall as the guards sleep, some believing that God will protect them. Grendel, insatiable for blood, moves quickly over the moors to Heorot. Feeling outcast and alone, Grendel’s anger builds up inside, and he imagines the havoc he will wreak. Little does he know this night will be different from all the ones before. Beowulf observes and waits, watching the monster eat one of his men greedily. Grendel plans to make Beowulf his next victim, but the hero grabs and startles him. Grendel is shocked by Beowulf’s immense strength; overpowered, the beast seeks escape. Beowulf and Grendel engage in hand-to-hand combat, throwing each other all around the hall, which stands strong despite the violent upheaval. The men in the hall hear a startling, inhuman cry come from Grendel who has been stricken with a serious blow; however, Beowulf does not let up. As Beowulf’s men join in to help defeat the beast, they realize “that no blade on earth … could ever damage their demon opponent.” The beast has magically removed “the harm” from all sword blades. 

Beowulf maintains his grip on Grendel, who feels the most severe pain he has ever experienced, as Beowulf pulls off the beast’s arm from the shoulder. The monster retreats to his lair and knows he will die; Beowulf has achieved what he set out to do in Hrothgar’s kingdom and made well on his promises. Beowulf hangs Grendel’s arm in the hall as a trophy, and the next day, warriors and chiefs arrive to see proof of the victory. Meanwhile, Grendel dies at “his marsh-den” and goes to hell. Beowulf’s prowess is exclaimed across the region, though Hrothgar is still respected as “a good king.” A bard sings a new song of Beowulf’s accomplishments, adding to his story of Sigemund the dragon-slayer, who gained fame after his death because he slew a dragon and won a great treasure hoard. 

Hrothgar and his queen arrive to see Beowulf’s trophy and proceed to thank God for allowing his kingdom the victory. He recalls the stress and grief under which his kingdom lived during Grendel’s reign of terror before praising Beowulf, God, and the mother who bore the great hero for the warrior’s strength, bravery, and achievements. Hrothgar claims Beowulf “as a dear son” and rewards him with treasures. Beowulf replies that he was “much favoured” in the battle with Beowulf and only wishes the king could have witnessed the monster’s defeat firsthand. He narrates an account of the final moments of battle and reveals that Grendel skulked away with a mortal wound. The defeat of Grendel shuts down Unferth’s critique of Beowulf, and everyone who sees Grendel’s arm hanging in Heorot is in awe of the hero.