When a blackened skeleton is unearthed on a building site in the City of London, no one can have the slightest idea of its extraordinary link to a plot to assassinate the Queen of Englandover 500 years ago. But there is one very conspicuous clue. On the index finger of the body's right hand is a gol...

When a blackened skeleton is unearthed on a building site in the City of London, no one can have the slightest idea of its extraordinary link to a plot to assassinate the Queen of Englandover 500 years ago. But there is one very conspicuous clue. On the index finger of the body's right hand is a gold ring topped with a brilliant, round emerald.