This book can be read as a stand-alone, but will read much better if you've read some of Joanna Bourne's previous novels in the Spymaster series, especially last year's The Forbidden Rose, where several of the novel's characters are introduced, and you get valuable backstory about this novel's main characters.
Sir Adrian Hawkhurst, head of the British Intelligence Service, opens the door his headquarters to find Justine DeCabrillac, former French spy, (who happens to be one of his childhood friends, his former lover and one of his fiercest enemies all wrapped up in one), bleeding to death on his doorstep. The dagger that stabbed her is one of his, and to make matters worse, she has been poisoned. Adrian is not about to let the woman he has loved for most of his life die, and as well as keeping her alive, he needs to find out who tried to kill her, why she ended up on his doorstep, and who is trying to frame him for her murder.
Much of the book is told in flashback, going back to the final days of the French Revolution, when Justine and Adrian, then a former London street rat known as Hawker, were children. They met when they were 13, Justine an agent for the French Secret Police, Hawker a fledgling spy for British Intelligence. While their friendship blossoms, they both know they are on opposite sides of a war, and can never truly become close. Justine gives her little sister to Doyle, Hawker's mentor, to raise, as she is eager that the girl escape the harsh and unforgiving life she herself has been forced into. Because of this, she runs into Hawker from time to time, when visiting her sister in secret, or on missions for France. The two become lovers, trusting each other despite their opposing loyalties.
The framework story takes place in 1818, after Napoleon is defeated, and imprisoned. France and England are no longer at war, and Justine has retired from her life of international intrigue. She's opened a shop in London, and for three years, Adrian has known where she is, but they have never approached each other. Now, finally seeing a chance to win her, once and for all, he needs to figure out why someone is intent on destroying them both, and convince Justine to stay with him for the rest of their lives.
I've read all of the books Joanna Bourne has in print, and this, her fourth in the Spymaster series, is by far my favourite. It helps that Adrian, as a supporting character in the other books, has more or less stolen every scene he is in. Yet with such high expectations, there was every chance that this book would turn out to be a huge disappointment. I'm so glad it actually surpassed my expectations. Justine and Hawker's romance is epic and all the more satisfying because they are separated for so long, and have to work so hard to reconcile their differences and find their happy ending.