On a visit to the ruins of Madderstone Abbey, Penelope Lambe suffers a bad fall and before she slips into unconsciousness, manages to say, “I saw her… It was her”. Some take these words to mean that Penelope saw the Grey Nun, the ghost reputed to haunt the abbey, but Miss Dido Kent is unconvinced and is determined to find the real cause. Dido directs all her mental energy to solving the mystery and revisits the ruins looking for clues. But events start to seem more sinister when a human skeleton is found at the abbey. But how is Miss Lambe’s accident connected to this discovery? Everyone is relying on Dido to find out.