Joyce Barnaby drives her car into a ditch, believing she has hit someone, but no-one is found hurt and husband DCI Tom Barnaby thinks she has imagined it. Then historian Ian Kent discovers the body of librarian Gerald Ebbs lying on a grave in March Magna cemetery. Joyce is convinced she is to blame for his death.


Gerald was clerk of the Parish Council and had few friends. He was obsessed with the cemetery, where people from all over the country who travelled to Midsomer in the 19th century to be treated for TB at the nearby sanatorium are buried. Meanwhile, Gerald's colleague at the library, Sarah Sharp, can barely conceal her joy at his demise.


Landlord Vic Bishop and his wife Mary tell Jones and Stephens that local ghost-walk organiser Jeff Bowmaker, who was in the cemetery on the night of Gerald's death, is a fake. Bowmaker claims the March Magna Inn where the Bishops work is haunted, because a former landlord slaughtered his family there before killing himself.


Barnaby learns from widowed florist Adam Peach and his daughter Jessica that Gerald regularly bought flowers to put on a girl's grave. It belongs to a young woman from Derbyshire who died in the 1870s. Meanwhile, Peach's son Liam steals flowers to give to Sarah Sharp.


Dr Bullard tells a relieved Barnaby that Gerald was killed by a piece of ornamental gravestone, not a car. But Joyce is still convinced that someone walked out in front of her, looking like a nun or a nurse.


In the graveyard, Bowmaker has a passionate encounter with Faith Kent, Ian's wife. The next day he goes to bed with Alice Carver, landlady of the B&B where he lives.


Barnaby and Jones visit the old sanatorium, now derelict. Faith, herself a local historian, reveals that a patient jumped to her death from the staircase, and since then the hospital was thought to be cursed. The dead girl was Caroline Roberts - whose grave was the subject of Gerald's devotion.


Joyce goes on a ghost-walk in a bid to find some answers, while Liam and Sarah head to the hospital to liven up Bowmaker's tour. Faith tells Bowmaker to be careful as Ian has hit her. But as the tour reaches the 'staircase of the damned', someone else falls to their death. Can Barnaby and Jones find out who is killing in March Magna - and why?