In Alexandria, Virginia in 2016 a young female lifeguard is raped while working at a local pool. Police learn of a similar incident in Fairfax, Virginia 2 years earlier. It takes ground-breaking genealogy tools to find the perpetrator.

In 1968, a 60-year-old is brutally raped and killed inside her own home. A devastating flood halts the police investigation until ground-breaking science offers new hope.