The Death Lesson

After the death of maths teacher Pippa Evans at an exclusive Welsh girls' school, police consultant Mallory Dawson is asked to go undercover to discover if the death was murder or suicide. Mallory discovers a trail of clues left by the dead teacher - puzzles that she can only solve with the help of super-bright student Livvy - which leads her to a horrifying discovery. One of the teachers is a former member of the Solstice Sisterhood, a women's group that was disbanded after reports of punishment and coercive behavior. But which teacher did Pippa recognise and why was the killer so desperate to keep her past from staff and pupils?