In 1992, Ruth and her husband buy a dilapidated house on Harris, intending to turn it into a guest house. They uncover a chest under some floorboards which holds the remains of a baby, its legs fused together almost like a mermaid's tail.
For personal reasons, Ruth feels compelled to investigate further. She never knew who her father was, and her mother drowned many years ago, after which Ruth passed through a succession of foster families and children's homes. Was her mother, she wonders, a selkie? Did she drown because some ancestral urge compelled her to return to the sea?
Back in 1860, the Reverend Alexander Ferguson is also wrestling with the mystery of selkies, from a different direction. Despite being a man of the cloth, he is taken with Darwin's theories, and wants to find evidence of land-dwelling humans who returned to the sea. He faces setbacks in the form of the laird's daughter, who takes a shine to him, and his inexperience in dealing with local politics.
There's a third narrator too: Moira, his maid, a native of the island, who has seen the landlord's men destroy her people's villages and force them to migrate in the name of profit. With both rage against the laird and love for Ferguson simmering inside her, Moira understands the island in a way the Reverend can't until it's too late.
All the narrators are such intriguing characters any one of them could be considered the lead. But Ruth's situation, and her fear of what her investigations might dredge up, is critical to the way Gifford reels us in: by building up the atmosphere as though it were a ghost story, she's got us hooked by the point we realise this is a different, more psychologically driven tale. The enchantment this novel casts on the reader, though, is very real.