Sally Spencer 
Blackstone and the Great War [EPUB ebook] 

The new Inspector Sam Blackstone mystery . . . France, World War One. Inspector Blackstone thought he was done with army, but when a general he served with requests he investigate the brutal murder of his grandson, a young British officer in the trenches, Blackstone feels he can’t say no. Surrounded by young men over half his age, Blackstone must face the horror of modern warfare, and the prejudices of the officer class, if he is to gain justice for the murdered man.