
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.

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.

The American serial killer Cesar Barone took the life of four women in and around Hillsboro, Oregon in the 1990s.

Lonnie David Franklin Jr. is better known by the nickname Grim Sleeper; he lures vulnerable women into his car before murdering and sexually assaulting them for more than two decades.