idolfi was an Italian banker who secretly used his position and many contacts in England to plot the assassination of Elizabeth and her replacement by Mary Queen of Scots. The so-called Ridolfi Plot had the backing of the Pope, Philip of Spain and Mary herself.
The Duke of Norfolk was drawn into treason by the hope of marrying Mary; and Philip ordered a Spanish invasion once the assassination was carried out.
While Ridolfi was organising matters abroad, Cecil and Walsingham discovered the plot. Norfolk was arrested and executed and the plot collapsed. Ridolfi returned to Florence where he lived out the rest of his life.