October 5th 1216: King John is in the Norfolk port of Lynn. On the same day but over 800 years later, Fiona 13 and Nick 10 move into Lamford Manor, a haunted Norfolk manor house. Incredibly, their lives are twisted together into a single adventure through an evil presence that haunts the old house. Fiona and Nick team up with Edna the housekeeper, their great aunt Daphne (Gad) and Jess their dog to confront the ghost and through a series of spooky clues they discover
a skeleton in a crumbling tunnel that appears to lead to the village church. First to explore the tunnel, Fiona and Nick step out into the medieval village of Lamford. First to arrive, Fiona and Nick find Sir Ralph Alleyn and his family living in the Great Hall, on the site of their manor house. When they hear Sir Ralph tell his wife, Lady Mathilda that their son, Hugh, is held hostage by King John in Lynn, Nick, as warranty for the completion of a secret mission. With the mission completed, he is set to ride back to Lynn, but, when he recognises that Nick could be easily be mistaken for Hugh, he sees his arrival as a sign from God. Nick must ride with him to rescue Hugh! They leave at dawn as Edna and Gad emerge from the church. Fiona persuades Lady Mathilda to open the Great Hall gates, but when Jess follows them in, the village believe devil in the guise of a black dog has entered the Great Hall. Men who would laugh at such rumours have yet to return from taking the harvest to market, so Young Tom, the blacksmith's son is the only one brave enough to help Lady Mathilda and her three daughters. Fiona forms a friendship with, Blanche the eldest daughter and through her with Young Tom.

Nick, who is well into medieval history, knows that by the time they reached Lynn, the king and his baggage train will have left and met with disaster in the Wellstream estuary. They don't catch-up with King John until he's on his deathbed in Newark Castle. Seeking redemption he asks to see his hostage, but Hugh has been abducted by Sir Guy Grosnez, an accomplice in many of the kings evil deeds. Nick is mistaken for Hugh and presented to the king. A loyal member of the royal household knows of Sir Ralph's secret mission and is sure Sir Guy is on his way to Lamford, but the race to save Hugh and the village can't begin until after the king dies. Grosnez arrives in Lynn and spreads the lie that King John has made a miraculous recovery and hires an army of mercenaries in his name in Lynn. From Lamford church tower, Young Tom sees them coming and warns the village. He also manages to tell Lady Mathilda that Master Hugh is with them, with hs hands bound to a saddle. Fiona joins him with all the arrows they can find and fletches them for him as he causes damage and confusion with his longbow.

Sir Ralph arrives with Nick and reinforcements to see the roof of the Great Hall on fire! The only way to escape is down a secret stairway into the tunnel beneath the house, where, as the battle rages above them they see King John's lost treasure, including the fabled Sword of Tristrum.