On the August Bank Holiday weekend of 1948 Joan Woodhouse, a demure, deeply religious London librarian, left her lodgings in London to visit the family home in Barnsley, Yorkshire. She never arrived. A week later her body, raped and strangled, was discovered in the grounds of the historic Arundel Castle in Sussex. Scotland Yard's elite murder squad were summoned and so began a two-year, still unresolved, saga that captivated press and public alike. Martin Knight here attempts to answer whether an innocent suspect nearly faced the hangman or a murderer went free.