Note, spoilers for the first two books lie ahead.
This is the concluding part of the Night's Masque trilogy, following on from The Alchemist of Souls and The Merchant of Dreams in which Mal Catlyn, impoverished sword for hire, became an Elizabethan spy, knighted for his efforts and now, at last, with his old home reinstated, his brother returned to sanity, a wife and an adopted son.
But this is not a straightforward historical story, so into the mix add a magical race of skraylings, beings discovered in the New World, and the threat of guisers, skrayling souls inhabiting human bodies and plotting to take over England. Indeed, one of them, Jathekkil, the main antagonist in the first book, died and has been reborn into the body of Queen Elizabeth's grandchild, and is now in line to inherit the throne – sooner rather than later once his father and older brother can be eliminated. (Yes in this version of history good Queen Bess married and had heirs.)
It's further complicated by the fact that Mal and his twin brother, Sandy, share a split skrayling soul between them. Sandy got the greater part and this is what led to him being considered mad for many years. So what's the difference between Mal and Sandy and the evil guisers? Simple, Mal and Sandy acquired the soul of the skrayling, Erishen, by accident and are not plotting against the crown, but trying to save it. There's also one further complication in that Mal's adopted son bears another skrayling soul, that of Kiiren, Erishen's long-time partner.
Got that? Good. That's the situation as this book opens.
The action starts quickly. Mal is quickly drawn into turmoil again as a bad decision he made in the second book, pops up to bite him on the bum when a powerful guiser from Venice appears at the Elizabethan court and becomes embroiled in young Jathekkil's plot to take the throne. Mal has to get rid of the guisers, but that involves killing what appears to be a small child, and that never looks good on your CV even if you're a spy.
At last Mal is learning to use skrayling magic and traverse the dreamlands, courtesy of Sandy's teaching and Erishen's soul. In this book he fights with magic as much as with steel.
Mal's son, Kit (Kiiren) becomes a pawn in the game as yet another player takes the field, this time with a mixture of skrayling and human magic that gives him a big advantage. Mal, Coby and Sandy, plus Mal's friends Gabriel and Ned, a gay couple who have been a major part of the team throughout the three books, take to the road in pursuit of Kit.
Ms Lyle handles the gay aspects of this book well, not only Gabriel and Ned but also the echoes of Mal's previous relationship with Ned.
There's a satisfactory conclusion and Mal retrieves the mistakes he made in the last book (by the skin of his teeth), though the victory is bittersweet. I feel sorry for Mal's wife, Coby, (though Coby's not the kind of character to feel sorry for herself) as she thought she married Mal and finds she got more in the package than she expected. She's the uncomplaining heroine of this piece.