Dafydd is an unassuming middle-aged schoolteacher in a sleepy Welsh village and a sketch artist of some note. In his spare time, he's a ruthless serial killer who believes Merlin speaks to him and instructs him in Chaos.

Devilishly clever and plausible, he evades capture but not suspicion, playing a game of cat-and-mouse with Llewellyn, a detective with a checkered reputation.Dafydd's wife suspects him and bears the brunt of many of his small tortures, until a freak set of circumstances beging bringing Dafydd undone.