After Beowulf defeats Grendel and Grendel's mother, he returns to his homeland. He is rewarded as a great warrior. Eventually, the ruling king is killed and Beowulf takes over the throne. He rules well for 50 years.
Unfortunately, a dragon has to emerge and ruin it all. The dragon is killing everyone and destroying everything. Beowulf and a group of warriors go to find the dragon and slay it. Beowulf puts up a good fight and wounds the dragon several times, but doesn't kill it. In fact the dragon even breaks his sword. All of the warriors have run away too (except Wiglaf). Together Beowulf and Wiglaf continue to fight the dragon, and the dragon succeeds in biting Beowulf on the neck and poisoning him.
He bit Beowulf's neck
with sharp tusks--Beowulf
was wet with life's blood;
blood gushed in waves.
Beowulf then succeeds in pulling out his knife and slaying the dragon. As Beowulf is laying there dying, he turns the throne over to Wiglaf and explains his burial wishes.