In Denmark, a very prosperous and popular ruler, King Hrothgar, has built a large mead hall and encouraged all of his soldiers to be jubilant and merry. The commotion from the festivities has greatly upset a horrible demon, Grendel, who lives in the swamp. Every night the demon terrorizes the community forcing the Danes to suffer at the hand of the beast for many years until a young Geatish warrior, Beowulf, hears of the plight King Hrothgar has endured.

Beowulf agrees to kill the Grendel, as repayment of a debt owed by his father to the King, who gratefully accepts. King Hrothgar throws a feast in Beowulf's honor that is interrupted by Grendel. A battle ensues between the monster and an unarmed Beowulf who is much stronger than the beast. Beowulf rips Grendel's arm off, sending him back into the swamp to die making Beowulf a hero.

Grendel's mother is the swamp hag, and upon finding her son's body, goes to the town seeking retribution. Beowulf, accompanied by soldiers, chases the creature back to the swamps where he dives into the water down to the hag's lair. He carries with him a powerful weapon forged for a giant and ends up victorious against the swamp hag. Beowulf's story goes on to describe a life where he ruled Geat for 50 years and was beloved by his people forever.