While investigating the brutal attack on Gregor, a seemingly single man, DS Joanna Harper discovers that her estranged daughter Ruby is somehow involved in this case that is steeped in Celtic mythology.

In a small seaside town a little girl is found alone; a woman arrives for her, and authorities release the pair, believing it to be an innocent case of a toddler running off. A man is found bludgeoned and left for dead in his apartment; the discovery of children's toys raises more questions than answers. Gazing into Gregor’s apartment, Ruby discovers his secret family: his unusually silent daughter and his mentally unstable wife, Constance, who insists that she is descended from the mythological Selkies. She begs Ruby to aid in finding the sealskin that Gregor has hidden from her, making it impossible to return to her people. When DS Joanna Harper's investigation into Gregor's assault leads her to CCTV footage of the mother-daughter pair from town, she realizes she knows the woman almost as well as she knows herself: it's her estranged daughter, Ruby. No matter the depth of Ruby's involvement, Harper knows she will choose her daughter over her career. -- adapted from jacket