
World's Most Evil Killers delves straight into the stories of the world's most prolific killers. Each episode focuses on one notorious killer and features first-hand accounts of their behavior; such killers range from Fred and Rose West, Ed Gein, the Clown Killer, to the Milwaukee Cannibal. Accounts are also given by detectives who ran the cases, journalists who reported on them, relatives, experts on analysis, and sometimes even survivors.

The story of the Beltway sniper attacks; John Allen and his teenage accomplice carry out a brutal series of shootings that kill ten people.

One of the most prolific serial killers in Canadian history is dubbed "The Pig Farmer Killer" by the media.

Joanne Dennehy violently stabs three men to death in March 2013; she kills for her own entertainment and is diagnosed as a psychotic sadomasochist.

Beverley Allitt killed four children and attempted to murder nine more while working as a nurse at Grantham and Kesteven Hospital in Lincolnshire, England, in 1991.