"Mary, Queen of Scots, is a Catholic and the great-granddaughter of Henry VII. This gives her the strongest hereditary claim to succeed Elizabeth I of England, who is Protestant, unmarried and childless.
In 1567, Mary was forced to abdicate the Scottish throne in favour of her infant son, James VI, who was raised Protestant. In 1568 she fled to England, where Elizabeth has held her in custody for 19 years.
In 1570, the Pope excommunicated Elizabeth and released English Catholics from obedience to her. Several plots since then have aimed to kill Elizabeth and place Mary on the throne. In 1585, Parliament passed the Act for the Queen's Safety, which allows anyone in whose name such a plot is made to be tried.
In 1586, Elizabeth's spymaster, Francis Walsingham, intercepted letters in which Mary appeared to approve a plot to assassinate Elizabeth (the Babington Plot). An English commission tried Mary, a foreign sovereign, and found her guilty.
England is in an undeclared conflict with Catholic Spain under Philip II, having sent troops to support Protestant rebels in the Spanish Netherlands in 1585.
It is February 1587. Elizabeth must decide whether to sign Mary's death warrant."