In 1982, seven people, mostly in and around Chicago, suddenly died without explanation. Eventually a nurse noticed a common thread between the deaths: the victims all taken the common pain reliever Tylenol - but their capsules were laced with cyanide.

This revelation started a frantic search to find the person responsible as fear spread across the country and store owners pulled Tylenol from their shelves. The case tortured families, a city, and a nation for decades.

The series follows investigators as they focus in on a key suspect, James Lewis, after meticulously piecing together other crimes to which he was connected, including extortion, dismemberment and another murder.

Four decades later, past clues and new technology raise the question: Could DNA evidence finally nail the killer?