`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 firsthand accounts of their behaviour; 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 crime analysis, and sometimes even survivors.