Grendel attacks Hrothgar's mead hall "Herot", filled with the Danes celebrating. Grendel is jealous of the celebrations, and massacres almost all of the Danes in the hall.
Beowulf, a great warrior and a prince of the Geats, brings together the best men he knows to help Hrothgar; as he helped his family before.
The Battle with Grendel's Mother
Grendel arrives back at Herot, as he expects to satisfy his thirst for blood; but he's faced with Beowulf. Beowulf proceeds to beat him in honorable hand-to-hand combat and rips off Grendel's arm.
Beowulf's Last Battle
Grendel's mother learns of her son's passing, then fueled by the need for vengeance; she arrives in Herot. She slaughters many Danes including Hrothgar's close friend.
Hrothgar informs Beowulf of the losses he has suffered, and Beowulf goes to challenge the mother of the monster he had previously vanquished. He eventually decapitates her and takes Grendel's head.
50 years later, Beowulf has become the king of the Geats and rules in peace and prosperity. A dragon is eventually disturbed by a thief and Beowulf dies honorably defeating the creature who threatened his kingdom.