The Fisher Folk were once plentiful in centuries past, until the witch-doctor of the tribes, Oona, fell in love with a human fisherman and together they produced a half-breed child. Enraged with this act of violation the Lords of the Deep, spirit-lords of the oceans, killed the fisherman and Oona committed suicide. Cheated of revenge, the Lords of the Deep turned to the Fisher Folks and condemned all the mothers and their newborns to die in childbirth, meaning that the tribes would never prosper. Nelda's own mother fell victim to this terrible fate along with so many other female Aufwaders. Meanwhile, a newcomer in town, Mrs Rowena Cooper, opens up a new antiques shop, and begins making herself very popular with the Whitby residents, by donating large sums of money to charity and charming even the most disagreeable neighbours. After being invited to tea at Mrs Cooper's house, Miss Boston and Mrs Joyster are instantly suspicious; Mrs Cooper appears ditzy, childish and too friendly for their liking. However, she has managed to woo over Miss Whethers, Miss Droon and Mrs Banbury-Scott most of all, whom she practically force-feeds expensive chocolates. After they leave, Miss Boston and Mrs Joyster share their doubts about Mrs Cooper, and Mrs Joyster is certain she has seen her before, but cannot recall where or when. She returns to her seaside cottage and reads her late husband's journal. In its pages, she discovers a horrifying truth: Rowena Cooper is in fact an evil woman named Roslyn Crosier, who, along with her diabolical husband Nathan, tormented and tortured an African tribe, inflicting unspeakable cruelty on them using black magic. The journal briefly mentions a gigantic black dog which terrified the tribe. Overcome with fury, she confronts Cooper, who reveals the truth of her identity and mocks Prudence, who is killed on the way home when an enormous black dog attacks her. Ben discovers that Nelda fears for her missing father, especially as a corpse has been discovered and has been identified as her uncle, Silas, a fiendish member of the tribe, and Hesper's husband. Hesper and Nelda tell Ben that they are searching for the moon kelp, a magical plant stolen from the Lords of the Deep, and if returned, the Deep Ones will grant the wish of anyone who finds it. Hesper wants to use it to lift the curse from the tribe. Shortly after Prudence's