In Episode 1, retired Detective Inspector Pat Marry takes us back to 2001, when, while still a sergeant in Balbriggan, he was put in charge of his first murder investigation.The victim was 27-year-old Mary Gough, who was declared dead after apparently falling down the stairs in the house she shared with her husband. Twenty years later, and with exclusive access to the original crime scene evidence, Det Insp Marry takes viewers through each step of the investigation, revealing what it taught him about being a detective.