I'm a fan of the Daisy Dalrymple series, and this book was a nice distraction on a boring day, but I didn't find it as good as the others.
The description on the web page is a bit misleading. There are anonymous letters, but they don't contain any threats or demands, they just unnerve the recipients.
Daisy finds so many suspects that I found it a bit hard to keep track of them. The descriptions of the people involved are a bit shallow this time, and I didn't find any of the new characters particularly likeable (except Daisy's little nephew).
In the Daisy Dalrymple books you usually have one or two nice people who are strongly suspected and you keep thinking "I hope he/she didn't do it". This aspect is missing in this book, the one person that might fit this bill is not presented extensively enough to make you feel with her.
There aren't many fun passages either, and there is a row and a reconciliation between Daisy and Alec which doesn't seem very convincing. I also missed the banter between Alec and Daisy, and Alec's assistants Piper and Tring who usually lighten the mood don't show up either.
We get to know Belinda a bit better, but all in all I don't think you'd miss a lot if you skipped this book in the series.