Maisie began a maturation process in the last book, Messenger of Truth, by confronting the demons that still haunted her from the war. In An Incomplete Revenge, she buries one element of her past in the person of Simon Lynch. That's not really a spoiler — Simon's been dieing for five books now, and his presence has influenced Maisie all the way along. Her interaction with Simon's mother, and her realization that she would not have been Mrs. Simon Lynch after the war, both serve to help her grow. Her interactions with a band of gypsies, and the revelation of her own gypsy blood, expand the character.
We are learning more and more about Maisie Dobbs with each book, which is much better than learning everything about a character in the very first book of a series. Winspear continues to grow Maisie Dobbs, letting us see her warts and all, and that is the epitome of proper characterization.
There are questions left unanswered, which only makes me eager for book six. An Incomplete Revenge was a satisfying read, and is highly recommended. It's official: I'm a fan. The book is due out in February, so reserve yours at Amazon now.