Elizabeth I rose to the throne of England in 1558 after the relatively rapid succession of three previous monarchs.
There were many plots for her death or removal from the English throne, as is apt to occur in any monarchy.
Mary Queen of Scots was living in England under custody of Elizabeth I since her forced abdication of the Scottish throne in 1567.
After a Catholic uprising in Scotland with the aim to place Mary on the English throne, a papal bull, Regnans in Excelsis, was published in 1570 releasing all Catholics from allegiance to Elizabeth and threatening excommunication to any that continued in allegiance to Elizabeth.
Several Catholic persons, including Sir Anthony Babington of Derbyshire, were plotting to place Mary on the throne, and a series of letters between Mary and the conspirators showed that she knew of the plot.