The book started by meeting Beowulf in Geatland. Beowulf was the hero that helped Hrothgar, and they knew each other their whole lives.
Approach to the Inmost Cave
Grendel is all I have, I want revenge.
Beowulf was called by Hrothgar, King of the Danes. The mead-hall named Herot was attacked many times by an ugly monster named Grendel and Hrothgar needed Beowulf's help.
Beowulf and Grendel fight, and don't use any weapons. Beowulf rips off Grendel's arm off with his bare hands and Grendel is bleeding out. Beowulf gives the arm to Hrothgar and he hangs it in the mead hall. Grendel runs home and bleeds to death.
Grendel's mom heard about what happened to Grendel and wants to get revenge. She comes up from the underwater cave and kills Aschere, Hrothgar's most trusted advisor. She then gets Grendel's arm, and Beowulf goes after her.
Beowulf gets down to the underwater cave and battled Grendel's mom for a long time. He then ends up killing her with the sword that she had in her cave. Beowulf then grabs Grendel's head as a souvenior and goes back to the mead hall.
At the mead hall he gave Grendel's head to Hrothgar in victory. Hrothgar was so thankful he showered Beowulf with treasure and gifts. Beowulf then returns to his home in Geatland.