Hunting Shadows by Charles Todd

A man is shot outside the cathedral where a big society wedding is about to start. Soon after, a small-town solicitor running for Parliament is shot while giving a speech. When the local police can't figure out who's behind the killings, Scotland Yard is called in and that means another case for shell-shocked WWI vet, detective Ian Rutledge. Like the local cops, he has a hard time figuring out the connection between the two deaths, though he's certain there is one and it takes a lot of persistence and legwork to find it. And to find the killer.

Hunting Shadows is another in the excellent Inspector Rutledge series by mother-son writing team Charles Todd. If you love a good mystery, check this series out.