A Necessary End by Peter Robinson

Violence erupts at an anti-nuclear demonstration in Eastvale, leaving one policeman stabbed to death.
At first there are over a hundred suspects, but then things narrow down to the people who live on "Maggie's Farm", an isolated house high on the daleside. Among the suspects is Dennis Osmond, a social worker involved with Jenny Fuller, Inspector Banks's friend.
As if this isn't enough to cope with, Banks finds his freedom hampered by the appointment of an old enemy, Detective Superintendent Richard 'Dirty Dick' Burgess, to head the investigation.
Although officially warned off the case, the only way Banks can salvage his career is by beating Burgess to the killer...

Inspector Banks #3