The third book of a story began in Prospero's Children and continued in The Dragon Charmer.
The first book introduced us to a teenage girl, Fern, who discovers she has magical powers which link back to a stone in doomed Atlantis.
The second book follows her after she's grown, on the eve of her wedding, and how she is abducted by Morgus, a witch from Arthurian mythology, and trained in witchcraft. But Fern's power is too strong and she escapes leaving Morgus for dead.
In witchcraft things are never as they seem and Morgus is back, invicible, and wants Fern dead.
This book is far quicker paced than the other two and I found it a far more riveting read. It does focus more on Fern and, sadly, doesn't have as much about the mysterious Ragginbone or his past history (but maybe Jan will write about this in another book).
Without giving anything away about the story I don't consider this the closing part of a trilogy. Merely the conclusion of the story for now. It certainly wasn't the ending I was expecting and it's one that leaves me waiting eagerly for a fourth book.