With the aid of dramatised scenes and location-based interviews with leading historians, this film tells the riveting story of how, over an eight-week period in 1586, England's greatest spymaster used covert espionage techniques to foil a Catholic conspiracy to murder Queen Elizabeth I and engineered the execution of Mary Queen of Scots. Sir Francis Walsingham is recognised as one of history's master spies, thanks to the extraordinary trap that he set for Mary, Queen of Scots. Using a sophisticated network of double agents, informants, and secret codes he allowed Mary to believe that she was master-minding a plot to destroy Elizabeth. In fact, every move Mary made was tracked, by intercepting and decoding her correspondence. As a result, the Scots Queen was exposed as a threat to the Crown, and Walsingham was finally able to persuade Elizabeth to execute her. As the man who went on to prepare England's defences against the Spanish Armada, Walsingham should be a national hero. But his quiet brilliance is tinged with fanaticism. "Walsingham was responsible for protecting the Queen from assassination and he saw it as his duty to use every weapon in his arsenal," says historian John Cooper. So why was this dangerous prince of spies so dedicated to his Queen and country? In this tense documentary we'll explore new visual evidence that will transform our understanding of Walsingham's dark world. This will include forensic X-ray and dating analysis which will reveal a 'lost' image behind one of the best-known portraits of the wiliest Elizabethan. We'll also tell the story of one of the most successful and thrilling intelligence operations in English history through compelling, dramatised sequences.