Encyclopaedia Britannica, 11th Edition, "Bent, James" to "Bibirine" by Various

2. All fear being now removed, the Danish king and his followers pass

the night in Heorot, Beowulf and his comrades being lodged elsewhere. The hall is invaded by Grendel's mother, who kills and carries off one of the Danish nobles. Beowulf proceeds to the mere, and, armed with sword and corslet, plunges into the water. In a vaulted chamber under the waves, he fights with Grendel's mother, and kills her. In the vault he finds the corpse of Grendel; he cuts off the head, and brings it back in triumph.