In 2001, Kathleen Peterson is found dead at the foot of a staircase in her home. At first deemed an accident, police soon suspect the victim's husband.
Investigators discover that 16 years ago, Michael Peterson's friend Liz Ratliff also died at the bottom of a staircase, lying in a pool of blood.
The defence unveils what they claim is a sought-after piece of evidence. Shock revelations about an expert witness threaten to unravel the entire case.