During a family trip to the seaside, four young siblings inadvertently summon a mermaid who tells the children about her sister, taken prisoner by a circus and made to perform against her will. The children set out to liberate the incarcerated mermaid, and are subsequently taken by the sisters to their underwater kingdom. However, they soon find themselves embroiled in a struggle to stop a full-blown war and save their new companions from total annihilation. Edith Nesbit (1858 - 1924) was an English poet and author. She is perhaps best remembered for her children's literature, publishing more than 60 such books under the name E. Nesbit. She was also a political activist and co-founded the Fabian Society, which had a significant influence on the Labour Party and British politics in general. This fantastical tale would make for perfect bedtime reading material and is deserving of a place on any family bookshelf. Many vintage books such as this are becoming increasingly scarce and expensive. It is with this in mind that we are republishing this volume now in an affordable, modern, high-quality edition complete with a specially-commissioned new biography of the author.