Arthur Bright is a singer - he once came second in the final of TV show the Voice Factor but, other than that, has lived a spectacularly average and unsuccessful life. He spends most of his time travelling alone up and down the country performing at sparsely-attended gigs and trying to get lucky with women he imagines are his fans.
Thing is, just recently, there are certain elements of Arthur's life that have started to get a bit... strange. A man calling himself Merlin, who Arthur considers quite mad, is following him around the country. Merlin - or Derek Border, to give him his proper name - is convinced Arthur is King Arthur and is keen he wakes up to this undeniable fact. Derek/Merlin even has a sword he believes is Excalibur, a group of men loyal to him - Knights of the Round Table - and an adult movie actress he has paid to be Guinevere. Although this all sounds completely crazy to Arthur, there's something else. Animals have started talking to him - just a couple of seagulls at first, hailing him as Britain's "once and future king" but soon dogs, cats and even a lion at the zoo, too. Arthur fears for his sanity and attempts suicide.
That's when a supernatural terrorist calling herself Morgana le Fay blows up St Paul's Cathedral and Arthur's destiny finally becomes clear to him.