The dragon is in the cave, guarding the treasure left by anciet civilians.
A slave steals a cup from the dragon.
When the dragon realizes the cup is missing, he goes on a rampage to find it.
Beowulf decided to fight the dragon even though he is old. He used the sword called Naedling.
The dragon used its fire to melt Beowulf sword causing Beowulf to fight without a weapon.
When the dragon bites Beowulf, the poison from the blood causes Beowulf to die. Wiglaf was the only one to come and help Beowulf fight and later was sent back to the cave to get some treasure so Beowulf could see it.