Set in the town of Spring Hill, Connecticut, The Winter Sister introduces Sylvie, loving sister of Persephone, a wayward teenage girl named after the sweet daughter of goddess Demeter, who was kidnapped by Hades and later became the Queen of the Underworld. Sylvie and Persephone have the type of relationship that seems externally fine, but beneath the routine of their daily lives are real problems. Persephone has been sneaking out at night to meet the mayor's son, Ben Emory. Persephone fails to come home one night. In blind panic, her mother, Annie, and her sister Jill decide to call the police. Sylvie tells DI Falley and DI Parker, the two detectives assigned to the case, that she thinks Ben would never hurt Persephone.
In any other context, Sylvie and Persephone would have a normal relationship with trials and tribulations recognized by millions. But as Collins' novel morphs into a murder mystery, these characteristics point to ambiguity and instability. Is Sylvie is trying to protect herself? No one--neither Jill, Annie, nor the detectives--notice the splotches of blue and gray on her fingers or the flashes of red near her nails. They fail to connect it to the painted moon over the first of the bruises on the surface of Persephone's skin. Sylvie is haunted by her last sighting of her sister and the expression on Persephone's face, "her breath making ghosts on the glass as she called her name."
Persephone's body is eventually found, bruising on her neck suggesting strangulation. Annie descends into an alcoholic stupor, retreating behind the locked door of her bedroom, back toward Ben's car, fresh snow sparkling on her coat. Sixteen years later, Persephone's murder has gone cold. The snow that compromised the crime scene made the chance of finding DNA evidence nearly nonexistent. But Sylvie is still plagued by the guilt that she didn't keep the bedroom window open and kept on swallowing Persephone's secrets night after night. Forced by Jill to return to retuned to Spring Hill to help out with Annie's cancer, Sylvie finally has to "just step up." So much has changed since that day in the incident room, yet even now the details of Persephone's death remain a mystery.
Sylvie's past circles around out of reach. After unexpectedly reconnecting with Ben, who now works as a nurse in Annie's care facility, Sylvie feels her life and the mystery surrounding Persephone's death slipping even further away. Was Persephone's love for Ben corrupted by contempt? Is Ben's sincerity alone sufficient to offer him full protection from Sylvie's wrath? Dying Annie's love for Sylvie is like "a dangerous animal." Ben loved Persephone but he had bruised her, "stained her skin with his pain." Persephone led him on and even encouraged him. For years, there was nobody to hear Ben's apologies, nobody to forgive him, "nobody to bear his grief or love."
Sylvie thinks of the secrets of her childhood home and how Persephone's ghost has led her back to this place. Like Bronte's Wuthering Heights, Collins writes a remarkable tale of two doomed lovers, a tragic, fragile "winter sister" and her guilt-ridden sibling who must learn once again to navigate through the happiness and heartbreak that life inevitably brings.