I enjoy all Nora Roberts books, including those she writes as JD Robb. I enjoyed this first book in a new trilogy, however I thought that the story theme was very like her Three Sisters trilogy which I read a long time ago, more like that than the Pagan Stone trilogy as another reviewer states. This time it is set in Ireland instead of America, although there is an American cousin, Iona. This first book, Iona's story is not nearly as menacing as the first in the Three Sisters trilogy, which perhaps lets it down somewhat.
Iona is sunny and bright in personality and having discovered that she is an ancestor of the 13C Dark Witch, which she hears about from her Irish grandmother, and realising that she has magick gifts, she goes to Ireland to meet her two cousins who have already been practising magick for years. The Dark Witch had three children and now that the three cousins are together, the dark sorcerer who wanted Sorcha, the Dark Witch's power, rises again.
Like the Three Sisters trilogy there is a 4th with power. Finn, the friend of the others, and like the Three Sisters there is s problem stopping Finn and Breanna, one of the cousins, coming together even though they love each other. Here, the problem, which I don't intend to divulge, is quite a clever twist.
It's an enjoyable read, even though she is resurrecting old story lines. However, she has done that before with some of her other trilogies e.g. The Pagan Stone trilogy is very similar to The Key of Knowledge trilogy.
NR has also made an historical bloomer in Chapter 1. Potatoes were not introduced into Europe from the Americas until approximately 16C. So Sorcha and her children would not be eating them in Ireland in 13C.