King Hrothgar was enjoying his reign. The king and and the Danes would gather in his mead hall, where they would feast and sing.
One night, Grendel walks into the mead hall and devoured and slayed thirty sleeping Danes. For the next 12 years, Grendel prevents anybody from entering the mead hall, causing Hrothgar to despair.
From accross the sea, word reaches the Geats of King Hrothgar's problems and they send Beowulf and his men to give help to the Danes.
Beowulf and his men head into the mead hall to wait for Grendel to appear. He snatches up one of the men to eat him and tries to grab Beowulf. Beowulf reaches up and rips off Grendel's arm. He fleas and leaves a trail of blood. The men rejoice knowing Grendel is dead.
Later that night, Grendel's mother goes into the mead hall to avenge her son's death. She is able to grab one soldier and her son's arm but she flees when she realizes that she cannot defeat Beowulf.
Beowulf and his men follow her into her underground lair. He finds a sword, shining with the light from God, and uses it to defeat her. King Hrothgar is happy and give Beowulf and his men gifts.