Margot is having a thirtysomething crisis: She's burning out at work, a public health practice; she's just left her longtime boyfriend after discovering he was cheating; and her mother recently died. The only silver lining to her mother's death is that Margot, who was adopted, can finally go looking for her birth mother. What she finds is an incomplete family; the only person left is Nikki, her mother's older sister. Aunt Nikki brings upsetting news: Margot's mother is dead, murdered many years ago, one of a series of sex workers killed in Glasgow. The killer has never been found, Aunt Nikki claims. They're still at large and sending her letters, gloating letters with details of the crime. Now Margot must choose: take the side of the world against her dead mother, or investigate her murder and see that justice is done at last.