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, then kills 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 begins in medias res or simply, "in the middle of things", a characteristic of the epics of antiquity. Although the poem begins with Beowulf's arrival, Grendel's attacks have been ongoing. 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 brotherhood linked by loyalty to their lord. The poem begins and ends with funerals: at the beginning of the poem for Scyld Scefing and at the end for Beowulf.
The poem is tightly structured. E. Carrigan shows the symmetry of its design in a model of its major components, with for instance the account of the killing of Grendel matching that of the killing of the dragon, the glory of the Danes matching the accounts of the Danish and Geatish courts.
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 Grendel's equal. 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 prevails, and Hrunting proves incapable of hurting her; 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. Its blade melts because of the monster's "hot blood", leaving only the hilt. Beowulf swims back up to the edge of the lake 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.
Final 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.
The poem contains many apparent digressions from the main story. These were found troublesome by early Beowulf scholars such as Frederick Klaeber, who wrote that they "interrupt the story", W. W. Lawrence, who stated that they "clog the action and distract attention from it", and W. P. Ker who found some "irrelevant ... possibly ... interpolations". More recent scholars from Adrien Bonjour onwards note that the digressions can all be explained as introductions or comparisons with elements of the main story; for instance, Beowulf's swimming home across the sea from Frisia carrying thirty sets of armour emphasises his heroic strength. The digressions can be divided into four groups, namely the Scyld narrative at the start; many descriptions of the Geats, including the Swedish–Geatish wars, the "Lay of the Last Survivor" in the style of another Old English poem, "The Wanderer", and Beowulf's dealings with the Geats such as his verbal contest with Unferth and his swimming duel with Breca, and the tale of Sigemund and the dragon; history and legend, including the fight at Finnsburg and the tale of Freawaru and Ingeld; and biblical tales such as the creation myth and Cain as ancestor of all monsters. The digressions provide a powerful impression of historical depth, imitated by Tolkien in The Lord of the Rings, a work that embodies many other elements from the poem.