In 1991, Massachusetts emergency personnel are called to the home of Richard Alfredo, who was slumped over dead of an apparent heart attack. No one thought foul play was a possibility until police looked into odd behavior of his girlfriend Christina Martin in the days before his death. Controversy surrounded the case for almost a decade, which pitted competing teams of toxicologists against each other -- one claiming the death was natural and the other saying it was cold-blooded murder.