Every Monday evening, six people gather in a smart North London house to talk about addiction. There they share their deepest secrets: stories of lies, regret, and above all, shame. Then one of them is killed - and it's clear one of the circle was responsible. Detective Inspector Nicola Tanner quickly finds her investigation hampered by the strict confidentiality that binds these people and their therapist together. So what could be shameful enough to cost someone their life? And how do you find the truth when denial and deception are second nature to all of your suspects?