June, 1510: the Burren, west coast of Ireland

King Turlough has departed to do battle against the Earl of Kildare when Mara goes into labour, unexpectedly early. She sends for Malachy the physician, but he does not arrive - only his estranged daughter, Nuala, comes to her aid. After the birth of a healthy son, Mara quickly regains strength, and then Nuala tells her the news: Malachy has been found dead, poisoned by one of his own medicines.

Malachy's new wife and her two sons stand to profit from his death, and Nuala herself is also a suspect in Mara's eyes. However, Mara soon discovers that there are many others who bear Malachy a grudge - he was not a good physician and had made many errors in diagnosis and treatment.

Mara and her scholars have their work cut out for them, if they are to find the murderer before the King returns to the Burren ...