A Midsummer Night's Death — K.M. Peyton

Jonathan doesn't like Robin, the English master at his boarding school. It's not his inability to control his classes that he dislikes, nor even his incompetence as a teacher - it's his complete indifference to the feelings of anyone but himself.

Nevertheless, Jonathan is stunned when it's announced that Robin has been found dead - drowned in the river close to the school. The coroner rules that it was suicide, but Jonathan soon comes to have reasons for doubting this...