American billionaire Arnold Crumble intends building a championship golf course and luxury hotel, on an English fens National Nature Reserve that has SSSI reserve status. Prompting doctor's disabled daughter Beverley, farmer's boxer son Josh, and youngsters Ben and Tim to form The Fenland Knights secret society. Based on the Knights Templar, using code-names, secret codes (written and digital) and membership cards, they vow to conquer. The junior members get into scrapes and have to be rescued. The reserve's Little Mere was restored by Josh and brother Tom. So when Tom goes missing in Afghanistan it becomes personal. Beverley hatches several sensible schemes, produces a petition, and even speaks to the Prime Minister, but sadly suffers some set-backs. However, when Tim and Ben rescue a little dog - have they found an answer? The outcome is an epic final battle.