By a Narrow Majority

the long version

"When a would-be politician is found battered to death in his kitchen, DI Hillary Greene is not convinced that the motive is political. After all, the victim was not universally popular in the small village where he lived, and it quickly transpires that he was having an affair. But then Hillary, working on another case, is abruptly and violently prevented from continuing with the murder investigation. Instead, another problem takes over all her time - a problem that could have serious ramifications for both herself, and her superiors. For Hillary knows only too well, cops don't like it when they themselves come under investigation."--BOOK JACKET.