Murder In Hindsight: Revised Edition - Paperback

Detective Sergeant Kathleen Doyle was almost certain they were dealing with a vigilante, in these seemingly-unrelated murders.
Each of the victims had been killed in the quiet confines of a London park, and each time, the victim was someone who'd been suspected of an earlier murder, but who'd managed to get off, for one reason or another.
So; who was making certain that justice was meted out, even if a bit belatedly?
Meanwhile, Acton seemed to be drinking a great deal, and dropping hints that they should visit his ancestral estate-it was almost more than a body could bear, on top of everything else.
Lucky, it was, that he'd never found out about how she'd been attacked, in the projects; after all, Acton was something of a vigilante, himself.