The Crossing of Ingo

Finally, my new novel has come after waiting for about two weeks! Usually, the online bookstore where I order some novels throw my me the books 3-4 days after I order them, but idk it took about two weeks to send this one, maybe it's out of stock.
Sooo, yeah, the title is The Crossing of Ingo. This book is the last from Ingo Series by Helen Dunmore (the first three are Ingo, The Tide Knot, The Deep). Actually, this novel is for children, but who cares? Harry Potter also for children, but almost everybody in this world love it. This novel is about a great adventure of a girl called Sapphire and her brother-Connor in the ocean. They're half human and half Mer (Mer is like mermaid, but Sapphire and Connor don't have mermaids' body). Any question? What about their adventure? Just read this series :D