The protagonist Beowulf, a hero of the Geats, comes to the aid of Hrothgar, king of the Danes, whose great hall, Heorot, is plagued by the monster Grendel. Beowulf kills Grendel with his bare hands and Grendel's mother with a giant's sword that he found in her lair.
Later in his life, Beowulf becomes king of the Geats, and finds his realm terrorized by a dragon, some of whose treasure had been stolen from his hoard in a burial mound. He attacks the dragon with the help of his thegns or servants, but they do not succeed. Beowulf decides to follow the dragon to its lair at Earnanæs, but only his young Swedish relative Wiglaf, whose name means "remnant of valour",[a] dares to join him. Beowulf finally slays the dragon, but is mortally wounded in the struggle. He is cremated and a burial mound by the sea is erected in his honour.
Beowulf is considered an epic poem in that the main character is a hero who travels great distances to prove his strength at impossible odds against supernatural demons and beasts. The poem also begins in medias res or simply, "in the middle of things," which is a characteristic of the epics of antiquity. Although the poem begins with Beowulf's arrival, Grendel's attacks have been an ongoing event. An elaborate history of characters and their lineages is spoken of, as well as their interactions with each other, debts owed and repaid, and deeds of valour. The warriors form a kind of brotherhood linked by loyalty to their lord. The poem begins and ends with funerals: at the beginning of the poem for Scyld Scefing (26–45) and at the end for Beowulf (3140–3170).
First battle: Grendel
Beowulf begins with the story of Hrothgar, who constructed the great hall Heorot for himself and his warriors. In it, he, his wife Wealhtheow, and his warriors spend their time singing and celebrating. Grendel, a troll-like monster said to be descended from the biblical Cain, is pained by the sounds of joy. Grendel attacks the hall and kills and devours many of Hrothgar's warriors while they sleep. Hrothgar and his people, helpless against Grendel, abandon Heorot.
Beowulf, a young warrior from Geatland, hears of Hrothgar's troubles and with his king's permission leaves his homeland to assist Hrothgar.
Beowulf and his men spend the night in Heorot. Beowulf refuses to use any weapon because he holds himself to be the equal of Grendel. When Grendel enters the hall, Beowulf, who has been feigning sleep, leaps up to clench Grendel's hand. Grendel and Beowulf battle each other violently. Beowulf's retainers draw their swords and rush to his aid, but their blades cannot pierce Grendel's skin. Finally, Beowulf tears Grendel's arm from his body at the shoulder and Grendel runs to his home in the marshes where he dies. Beowulf displays "the whole of Grendel's shoulder and arm, his awesome grasp" for all to see at Heorot. This display would fuel Grendel's mother's anger in revenge.
Second battle: Grendel's mother
The next night, after celebrating Grendel's defeat, Hrothgar and his men sleep in Heorot. Grendel's mother, angry that her son has been killed, sets out to get revenge. "Beowulf was elsewhere. Earlier, after the award of treasure, The Geat had been given another lodging"; his assistance would be absent in this battle. Grendel's mother violently kills Æschere, who is Hrothgar's most loyal fighter, and escapes.
Hrothgar, Beowulf, and their men track Grendel's mother to her lair under a lake. Unferð, a warrior who had earlier challenged him, presents Beowulf with his sword Hrunting. After stipulating a number of conditions to Hrothgar in case of his death (including the taking in of his kinsmen and the inheritance by Unferth of Beowulf's estate), Beowulf jumps into the lake, and while harassed by water monsters gets to the bottom, where he finds a cavern. Grendel's mother pulls him in, and she and Beowulf engage in fierce combat.
At first, Grendel's mother appears to prevail, and Hrunting proves incapable of hurting the woman; she throws Beowulf to the ground and, sitting astride him, tries to kill him with a short sword, but Beowulf is saved by his armour. Beowulf spots another sword, hanging on the wall and apparently made for giants, and cuts her head off with it. Travelling further into Grendel's mother's lair, Beowulf discovers Grendel's corpse and severs his head with the sword, whose blade melts because of the "hot blood". Only the hilt remains. Beowulf swims back up to the rim of the pond where his men wait. Carrying the hilt of the sword and Grendel's head, he presents them to Hrothgar upon his return to Heorot. Hrothgar gives Beowulf many gifts, including the sword Nægling, his family's heirloom. The events prompt a long reflection by the king, sometimes referred to as "Hrothgar's sermon", in which he urges Beowulf to be wary of pride and to reward his thegns.
Third battle: The dragon
Beowulf returns home and eventually becomes king of his own people. One day, fifty years after Beowulf's battle with Grendel's mother, a slave steals a golden cup from the lair of a dragon at Earnanæs. When the dragon sees that the cup has been stolen, it leaves its cave in a rage, burning everything in sight. Beowulf and his warriors come to fight the dragon, but Beowulf tells his men that he will fight the dragon alone and that they should wait on the barrow. Beowulf descends to do battle with the dragon, but finds himself outmatched. His men, upon seeing this and fearing for their lives, retreat into the woods. One of his men, Wiglaf, however, in great distress at Beowulf's plight, comes to his aid. The two slay the dragon, but Beowulf is mortally wounded. After Beowulf dies, Wiglaf remains by his side, grief-stricken. When the rest of the men finally return, Wiglaf bitterly admonishes them, blaming their cowardice for Beowulf's death. Afterward, Beowulf is ritually burned on a great pyre in Geatland while his people wail and mourn him, fearing that without him, the Geats are defenceless against attacks from surrounding tribes. Afterwards, a barrow, visible from the sea, is built in his memory (Beowulf lines 2712–3182).