Explores the personality of the man behind the crimes - on the surface a mild-mannered civil servant who admitted to murdering up to 15 young men over a four-year period in the late 1980s and early 1980s, disposing of their bodies in the garden and down the drain. The film includes footage of an interview Nilsen gave to ITV at Albany Prison in 1992, contributions from victims' families and insights from criminologist David Wilson, who corresponded with Nilsen over several decades. Narrated by David Tennant.