After Grendel is slain by Beowulf, his mother immediately exacts a terrible vengeance. The Danes have been rejoicing at the death of the monster that had plagued them for so long and caused so much bloodshed and destruction. They celebrate Grendel's death in the traditional Danish manner by holding an enormous feast in the mead hall of Heorot. As the Danes are sleeping off their celebration, Grendel's mother descends upon Heorot like a wolf on the fold. She carries off Æschere, Hrothgar's most trusted advisor, a man of great wisdom and knowledge. Once back at her lair, she kills Æschere, ripping his head off for good measure. Later on in the poem, when Beowulf and his warriors head off to do battle with Grendel's mother they find Æschere's severed head at the entrance to her lair.
As Beowulf opens, the Danish king Hrothgar and his men had languished under fear of the demon Grendel for twelve years. Beowulf, a Geat, liberates the Danes from the monster's haunting by slaying him. Beowulf kills Grendel by ripping his arm out of its socket; he decides to keep as a trophy, and the Danes hang it in their mead-hall. Before Grendel died, he fled back to his lair. This did not trouble the Danes, because they knew he had been mortally wounded. They begin to celebrate
Unfortunately, the Danes did not realize Grendel had a relative. When Grendel's mother realized what had happened to her son, she determined to seek vengeance. She descends upon the Danish mead-hall, Heorot, in the middle of the night. She takes Grendel's arm, abducts one of the king's advisors, and then flees to her lair. Beowulf ultimately decides to infiltrate her lair and kill her as well.