When the first hate letter arrives in the aftermath of her patient Bonnie's death, obstetrician Dana Cavanagh reads it with shaking hands before placing it next to the small news article from the court's verdict: not guilty. Hate mail continues to trickle in, but one stands out from the others: a cryptic message with a tiny marble stone, its origins in Kos, Greece, the birthplace of Hippocrates. Dana had once proudly sworn his oath, 'I will give not deadly medicine.' Accompanied by her sister Madeleine, Dana follows the mystery of the letter to Kos. The arrival of two more letters, and the strange and ghostly appearances of a woman, beckon Dana to continue their journey further. Despairing for her sanity, can Dana persist in her crusade and come to terms with being implicated in the death of another?