This is the third and concluding book to the Three Sisters Island trilogy, and is indeed a fitting rounding off of the series. Sam Logan has returned to the Island, and he has much to resolve about his earlier relationship with Mia. For her part, as we've seen in the earlier books, although she doesn't realise it Mia is very alone. She does not want to risk loving again - certainly she does not want to risk loving Sam again. Now it is Mia's turn to face her trial, in order that Three Sisters Island be saved.
I didn't find many surprises here - the threat is by this time well known, and identified to all. However as usual the writing was great, the romance part evenly developed and I identified with Mia's reluctance to turn a simple relationship into something more. I enjoyed revisiting all the characters and getting to know Sam. I don't know that I found his reason for absence convincing - yes for why he left, but not for why he stayed away so long. However, that aside, I enjoyed the way the Three were working together - or, as is pointed out during the course of the book, the Six. Seven, really.
I think that one should read the previous two books for maximum effect, although the previous stories are alluded to here. For me the most enjoyment was meeting the characters again - by this time they are almost like friends.
I also liked that Mia is the strongest witch, including... well, read it for yourself.