In this three-part series for BBC Four, historian Helen Castor pieces together the astonishing true story of Lady Jane Grey - the first reigning Queen of England.

We may think we know the history: an innocent teen thrust onto the throne and beheaded as a traitor after reigning for just nine days. But Helen discovers original documents that reveal a Tudor thriller - an epic story of dynastic rivalry, intrigue and betrayal. A young woman manipulated by older men who ends up losing her life as a result.

In July 1553, Tudor England is rocked by a constitutional crisis. Henry VIII's young son Edward dies with no male heir to inherit the throne. Having never had a reigning Queen, England now has two who claim the title. Two women prepared to fight for the throne - the 37 year-old Catholic Mary Tudor and the teenage Protestant Jane Grey.