1930. Frances Black is worried - divorce proceedings are under way and her solicitor has learnt of a spiteful letter sent to the court claiming that there is more to her friendship with her sleuthing partner, Tom Dod, than meets the eye.

Fran takes Tom's advice to get away, travelling down to Devon to help the Edgertons with their family mystery. After meeting the charismatic Eddie Edgerton and arriving at their residence, Sunnyside House, Fran soon learns that Eddie's grandfather, Frederick Edgerton, died in mysterious circumstances when his wheelchair went off a cliff. Was it really an accident? And what happened to Frederick's precious diamond which went missing at the time of his death? As Fran investigates, she uncovers family scandal, skulduggery and revenge, but can she solve the mystery of the missing diamond?