The Dark Tide

 The Dark Tide by Alicia Jasinska, 336 pages.

Caldella is a magical island ruled by a witch queen. The island is sinking, and has been since it's founding hundreds of years ago. The only thing keeping the city afloat is the witch queen's sacrifice. Each year on St. Walpurga's eve she takes a boy from the celebrations, and on the next full moon she drowns him to save the city. Except for two years ago, when the queen sacrificed herself instead. 

Lina is convinced her handsome brother is going to be taken this year, despite all her efforts to stop him from going to the revel. When he goes anyway she goes in to save him, along with Thomas Lin, the boy she's had a crush on for years. Also the boy the witch queen sacrificed herself for two years ago. When Thomas is taken by the new witch queen (Eva, the younger sister of the last queen), Lina takes his place. But she didn't expect to develop feelings for the queen who allegedly threw her own heart into the sea. Even less did she expect those feelings to be reciprocated.

There are places in this book where it is very obvious that this was a debut novel. There are some rough edges and several points that require a pretty sizable scoop of suspension of disbelief. However, it more than makes up for it with a stunning sense of atmosphere. The whole book feels like a fairy tale, intensely magical and more than a little creepy. It borrows heavily from the ballad Tam Lin, but I don't know that I would go so far as to call it a retelling. It takes just enough to reinforce the classic fairy tale atmosphere, and there are plenty of times it almost feels like a dream. Definitely a thoroughly enjoyable book.