Answer
Mary, Queen of Scots, the renowned monarch of Scotland, met her tragic fate due to the diligent efforts of Francis Walsingham, the principal secretary to Queen Elizabeth I of England. Walsingham, a shrewd and resourceful statesman, meticulously gathered evidence against Mary, implicating her in plots to assassinate Queen Elizabeth. This led to Mary's eventual execution in 1587, solidifying Elizabeth's reign and thwarting any potential threats to the English throne.