Between Two Evils by Eva Dolan

As the country bakes under the relentless summer sun, a young doctor is found brutally murdered at his home in a picturesque Cambridgeshire village. Is his death connected to his private life - or his professional one? Dr Joshua Ainsworth worked at an all-female detention centre, one still recovering from a major scandal a few years before. Was he the whistle-blower - or an instigator? As Detective Sergeant Ferreira and Detective Inspector Zigic begin to painstakingly reconstruct Dr Ainsworth's last days, they uncover yet more secrets and more suspects. But this isn't the only case that's demanding their attention - a violent criminal has been released on a technicality and the police force know he will strike again: the only question is who will be his first victim...