The Roger the Chapman series was, for a long time, my favorite historical mystery series. However, the last 3-4 books have been big letdowns. Perhaps that's the inevitable fate of almost all long-running series.
This one "jumped the shark" for me when Roger started getting involved in Royal affairs. I found the stories so much more interesting when they involved the average people of medieval England rather than the machinations of Dukes and Kings and such.
This particular book -- the Medsummer Crown -- has several major flaws which go beyond simply my personal preference for normal folk: for the majority of the book, nothing of interest happens. Rogers walks around confused and inept, continually losing the people he's following, missing clues and moaning about the case. Then there are the totally incredible coincidences, like having the major suspects just happen to sit at the table behind him in an obscure London inn and discuss the entire case and their plans for him. I can't go into more details without revealing spoiling, but suffice it to say that it strains the reader's credulity to the breaking point.
Finally, the plot is extremely similar in many ways to the Green Man (again, I can't give details but many of the plot contrivances are EXACTLY the same and Roger even aludes to them in the book!) The ending is unsatisfying and implausible.
Sorry, Ms. Sedley. Your first dozen books were great and for them, I'll always be thankful. But here's where Roger Chapman and I part company.