Greenwild: The City Beyond the Sea by Pari Thomson

Daisy Thistledown is on a mission. She might have defeated a terrible enemy, but her journey to find her kidnapped mother is just beginning. After smuggling aboard a long-awaited expedition to the heart of theAmazon, Daisy and her friends soon find themselves in danger on the high seas, pursued across the waves by Grim Reapers.

Their only hope: to find the legendary Iffenwild, a mysterious city hidden beyond the sea and lost to time. But a strange, wild magic is stirring beneath the waves. It will take all of Daisy’s courage and determination – and the trust of a new friend – if she is to discover the truth that haunts Iffenwild, and save the magical world before it’s too late.