It's December in a small seaside town, and Ruby Harper spends her nights looking into her neighbor's apartment. Unable to sleep due to insomnia and the heartache of a family she has run away from, she fantasizes that the mystery man she watches could be the answer to her loneliness. But one night Ruby sees something unexpected: the man is not alone; a woman and a child are sharing the apartment, and they never go outside. Why are they kept hidden? Then the man is found half-drowned in the bathtub, a pile of women's clothes is left on the beach, and a little girl is discovered, abandoned. Detective Sergeant Joanna Harper is assigned to the case, which grows more complicated by the minute. Soon, a shocking revelation and a desperate bid for freedom put Ruby at the center of a crime, and hot on her trail is DS Harper, who knows her better than anyone and is ready to anticipate her every move.