Reeda Roundy and Betty Gray are found murdered in Roundy's home, along with a message written in blood, saying "Satan Loves You;" detectives piece together the stunning truth behind the murders with insights provided by the victims' families.

In Las Vegas, 41-year-old Nancy Menke, a mother of four, is found handcuffed and murdered in the passenger seat of her car; a records clerk in the insurance fraud unit stumbles upon a strange report that blows open Menke's murder case.