The Danes are soon to find that their triumph is not yet complete. Another danger lurks. Grendel's mother, who lives deep in the waters, is grief-stricken by her son's death, and seeks revenge.
As the Danes sleep, Grendel's mother comes to Heorot. She pounces on Aeschere, Hrothgar's most trusted friend, with the intention of taking him back to the fens.
Beowulf is not in the hall because he has been given a different lodging.
Grendel's mother snatches Grendel's claw. There is turmoil in Heorot as the news spreads. Beowulf is urgently summoned to Hrothgar. Hrothgar mourns the death of Aeschere, and knows that Grendel's mother has struck in order to avenge her son. He tells Beowulf what he has heard from his advisers about those two monsters. Grendel's mother looks vaguely like a woman. The country people say the ancestry of Grendel and his mother is hidden in a past of demons and ghosts. No one really knows where they come from. Then Hrothgar tells of a haunted mere, where at night the water burns. No man knows how deep it is. Even animals will not go below the surface of the mere. In storms, it throws up columns of dirty water to the sky. That is where Grendel's mother lives, and Hrothgar asks Beowulf, if he dares, to go there and kill her. He will be well rewarded if he succeeds.
As in the earlier episode with Grendel, mythology and fairy-tale take over the narrative here. Other parts of the epic allude to historical events and give clues to the nature of the warrior society, but the two monsters (as later the dragon) belong only to folklore. However, as he did in his initial description of Grendel, the poet tries to bridge the gap between the folklore element and the Biblical framework he has chosen for the epic. He does this by emphasizing once more that Grendel and his mother are the offspring of Cain, who killed his brother Abel, as the Book of Genesis tells. To make clear that the struggle between Beowulf and the monsters is one of good against evil in a Christian context, he points out-harping back to the earlier episode-that Beowulf overcame Grendel through his faith in God (lines 1271-73).