Nicholas Blake 
The Dreadful Hollow 

A VINTAGE MURDER MYSTERY
Someone is sending poison pen letters in the small village of Prior”s Umborne, and they have already driven one of the inhabitants to suicide.
Private detective Nigel Strangeways is commissioned to find the source of the letters by arrogant financier Sir Archibald Blick, whose two sons live in the village, only for Sir Archibald to meet an untimely end at the bottom of the dreadful hollow…
A Nigel Strangeways murder mystery – the perfect introduction to the most charming and erudite detective in Golden Age crime fiction.