I loved this book! The first 75-100 pages are a bit slow to start, telling the story of Saffron's birth and laying out the characters of her family, but once it switches to telling about Emer's life, it becomes pretty fast action. It's told in first person, from Saffron/Emer's perspective. It jumps between Saffron's modern day tale to Emer's story in the 1600's. I will warn that there is a bit of language content and it does deal a bit with homosexuality which doesn't really bother me, but might bother some.
I especially loved all of the story once Emer starts pirating. And there was a twist that I didn't see coming, so props to the author for pulling a fast one on me. I also loved the ending, which I won't comment on except to say that it was good without being too perfect.