What is the main plot of Beowulf (edited by M. A. Roberts)?

The plot of Beowulf is the heroic quest. In Beowulf's case, that quest is to claim his place in eternity. In Norse mythology, however, to gain admittance to "heaven" (Valhalla), the warrior must die in battle. Hrothgar should be the one to protect his own kingdom, but Beowulf, the outsider, has to do it for him. The fact that Beowulf fights the monster alone and unarmed makes his victory that much greater. You can think of Beowulf as the Viking equivalent of the Greek Heracles or the Roman Hercules.