(Some possible spoilers below)
This is an excellent read. I know a fair bit about this era, and I am a picky pedant when it comes to historical detail, but I could not find any errors at all. Not even the tiny flaws that sometimes jerk a picky pedant out of the moment but are relatively insubstantial.
It's no secret that King Henry IV is not my favourite Plantagenet. Indeed, if you drew up a league table, he would probably be hovering just above the relegation zone. His enigmatic personality makes him hard to write about and many authors have ducked it. Made him, for example, a supporting character in the story of his son.
Nevertheless, his life was a tragedy in the original sense, a gradual decline from being one of the most admired young knights of Europe to his final days as a very sick, very unpopular usurper king. From famous warrior and jouster to a wreck of a man who could not even sit a horse.
In this book - the rest of the series are recommended too - we see his final years. The beginning is set just after his victory at Shrewsbury, a few months before he became seriously ill. His suffering and frustration must evoke sympathy from the hardest heart. (No one knows what exactly was wrong with him but whatever it was it was extremely debilitating.)
On the other hand, the author does not attempt to whitewash the man. Henry was capable of ordering a traitor to be hanged repeatedly, but not fatally, in various towns before his ultimate execution. Then there was the famous case of Archbishop Scrope - the Scrope rebellion. by the way, being as well set out in this novel as in any work I have read, fact or fiction. Henry was not always political astute. His execution of Scrope was perhaps his biggest misstep. People of the time saw it as an explanation for the illness that made his life a misery.
The supporting characters are well-drawn too, Though you may find yourself wondering what on earth Northumberland was playing at. However, the earl's actions are in line with known facts. Queen Joan, who clearly loves her husband very much, is a quiet, loving presence in the background.
This is a book that I shall certainly re-read, along with the others inthe series.