1890: Jonathan Flaxton, the heir to Flaxton Hall, has disappeared. After making a secret visit to Jonathan's room, Peter Weekes becomes convinced he is still alive, and sets out to find him.
The Flaxton boys meet Barnaby Sweet, and together they foil a grim plot by the poachers of Carliston parish.
The Flaxton boys and their friend, Barnaby, are instrumental in freeing a servant girl from a life of drudgery.
The search for Jonathan Flaxton takes Peter and David to Harrogate; there they meet the beautiful Su Ling, who holds a vital clue to the mystery.
Peter and David discover that ghosts are not always invisible.
A faded photograph of a girl, set in a locket, leads the boys into an adventure in which Jack the Ripper has taken a hand.
There's trouble brewing with the local farmers for Sir Tarquin Stilgoe. Ironically, it is an innocent, sentimental valentine which leads them to the heart of the danger.
Dark shadows stalk the countryside as Vanessa Marden seeks her vengeance. A race against time now begins - with Andrew Flaxton's life at stake.
Sir Tarquin takes desperate measures when he realises the boys may discover the truth about the missing heir to Flaxton.
For intrigue and craftiness, old Molly Deever is unequalled - as Barnaby, who has been accused of horse-stealing is soon to learn.
Barnaby and Peter encounter two Irish rogues who are not all they appear to be.
A ship is due in Hull; a ship with an ominous yellow flag. Aboard might be a clue to the quest for the Flaxton heir - but Sir Tarquin and Jacklin lie between the boys and an answer.
Barnaby and the boys find their lives in jeopardy as they come closer to solving the mystery of Jonathan's disappearance.