Sapphire makes a deal with the Mer: if she and Conor help put the Kraken back to sleep their father will have the choice to leave Ingo.

After a battle of minds, Sapphire manages to get the Kraken to sleep, and with Conor and Faro she goes back to the Mer to tell them the good news.

Booklist reviewer Anne O'Malley praised the author's "fine writing", while Ruth Bamford found the book "easy to read and beautifully written".

[1][2] In a positive review, The Horn Book Magazine's Anita L. Burkham wrote, "Sapphire's picturesque life on the coast of Cornwall and the enchanting and perilous world underwater are depicted with equal depth and resonance in Dunmore's commanding prose.

"[3] The Sunday Times's Nicolette Jones liked the book's "sensual, descriptive prose that evokes the watery kingdom with conviction" and said the "characters are clear-cut and written with exuberance".