
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.

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.

John Wayne Gacy murdered 33 boys and young men during a six-year period in the 1970s; he was well-liked in the community he lived in and would often dress up for kids' parties, earning himself the nickname Killer Clown.

For 13 years, serial killer Jeffrey Dahmer raped, murdered and ate his young male victims; after his arrest, his apartment was searched and human skulls were found in his closet; he was killed by another inmate after serving two years in prison.