The Good Sister follows a couple who is working to put their crumbling marriage back together, when the wife receives a letter informing her that she has a long-lost twin sister. First thinking that the new family member will bring the couple closer together, the husband then begins an affair with the sister and discovers that she is treacherous and dangerous.

One cannot quench his all-consuming thirst. The other cannot tame the beast clawing its way out. In the sleepy Pennsylvania village of Hemlock Grove, two young men struggle to accept painful truths: about family, themselves, the mystery of the White Tower - and a terrifying new threat so powerful it will turn them from predators into prey.