Now I have stopped looking for it and don't need it I've found The Fears of Henry IV. Predictably it was within three feet of where I am sitting to write this, in a location where my eyes should fall at least once a day. Yesterday, mysteriously, it was there. I am sure it was not there before and yet logic tells me that it must have been. Spooky!
I haven't got the time or the inclination to do a full review at this time, but if you're at all interested in Henry Bolingbroke it's certainly worth buying. Frankly, it doesn't have much competition as decent books about him are rare. When I was working on Fetterlock my principal source for Henry's reign was History of England under Henry IV by J.H.Wylie. This was written in the late 19th century, and although it contains many details you're unlikely to find anywhere else it gives the impression it was hurriedly thrown together from sheafs of rough notes and chucked straight at the printer without benefit of editor. Ian Mortimer's book is much more suited to the needs of the 21st century reader, or indeed anyone who isn't a total history obsessive.
What I will say about Fears of Henry IV is it does come over as a bit of a hagiography. Mortimer makes no bones about the fact he is telling the tale from Henry's POV, and that's fair enough - probably a lot better than the pretended impartiality of so many historians. But do not open it with the expectation that Richard II will be cut any slack whatsoever, because he isn't. Mortimer clearly thinks he was worse than a thousand Hitlers.