When South London schoolboy Jamie goes to Wimbledon to photocopy some pictures for his school project on the Old English poem 'Beowulf', he little thinks that his life will never quite be the same again.
Deciding to exchange his bus fare home for a hamburger, Jamie somehow ends up in the company of a very weird old man for whom everything seems to have stopped in the time of the Anglo-Saxons.
After being thrown out of the hamburger bar for creating a disturbance, the pair heads for Wimbledon Common.
In between 'gathering tributes' of what seem to be other people's unattended food and drinks Grimm, the old man, tells Jamie what he claims to be an eye witness account of the story of Beowulf and the hero's battles with the monster Grendel and Grendel's mother in the damp of a Danish bog.
Although Grimm's version is not quite the same as that told in the poem he claims that it is all true, well almost true.