It is June 1897, and three years have passed since Rose McQuinn's husband, Danny, went missing in Arizona. Returning to England, she fulfilled her ambition of becoming a 'Lady Investigator, Discretion Guaranteed', and is about to marry her lover, Detective Inspector, Jack Macmerry, of the Edinburgh Police. But pre-wedding jitters become the least of her worries when a nun from the local convent claims to have received a letter from Danny. Is the elderly nun just confused, or is a ghost about to walk back into her life?