Six mermaids battle to save their hidden world. Leaders of a resistance to the barbaric new regime, Serafina and Neela, are working hard to destabilise Vallerio, the new ruler of Cerulea.Becca, Ava and Ling are still hunting for their ancestors' talismans; the keys to keeping an ancient evil locked in its icy prison.Astrid finally returns home to Ondalina to find that all is not as she left it, and a sinister human with empty, black eyes offers her power she never dreamed of ... The third book in the Waterfire Saga.