When an old castle needs renovating so that it can be opened to the public, Dr. Florence Mountfitchett of Local Heritage calls Bob the Builder to fix it. Unfortunately, a case of mistaken identity puts Bob's dad in charge of the job! Tales of the Knights of Camelot inspire Bob's noble team of machines to take on new identities, whilst Spud goes on a quest for a suit of armour! Bob's dad begins to trim the hedges of a maze - but ends up getting lost in it, whilst Bob discovers a secret door... Will Bob's dad ever find his way out of the maze? Does Bob discover what's behind the secret door? Can Bob and his team get the castle finished in time for the grand opening? Join Bob the Builder and his "Knights of Can-A-Lot" in their biggest adventure to date!