Wet Magic

When four siblings journey to the seashore for a holiday, one of them unwittingly summons the sister of a mermaid who is captured by a circus, and the children set out to save the imprisoned being. After a daring midnight rescue, the children's reward is an incredible journey beneath the waves and into the hidden kingdom of the mermaids. But they soon find themselves in a race against time as they struggle to prevent a war and save their new underwater companions...

Edith Nesbit (1858-1924) was an English poet and author. She is most well known for her children's literature, publishing more than 60 such books under the pen 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.