The scold's bridle

Mathilda Gillespie's body was found nearly two days after she had taken an overdose and slashed her wrists with a Stanley knife. But what shocked Dr Sarah Blakeney the most was the scold's bridle obscuring the dead woman’s face, a metal contraption grotesquely adorned with a garland of nettles and Michaelmas daisies. What happened at Cedar House in the tortured hours before Mathilda's death?
The police assume that the coroner will return a verdict of suicide. Only Dr Blakeney, it seems, doubts the verdict. Until it is discovered that Mathilda’s diaries have disappeared.