Campion was the most famous of the Jesuit martyrs. These courageous men were trained abroad and sent back to England to 'keep alive the Catholic faith'. They worked in secret, moving from house to house and running the risk of torture and death if caught.

The nature of their activities, once discovered, seemed to confirm fears of a widespread Catholic conspiracy in England.

Francis Throckmorton was a Catholic conspirator. Although his name is usually attached to the plot of 1583, he probably only acted as a 'go-between'.

The plan involved an invasion of England led by the Duke of Guise and paid for by Philip of Spain and the Pope. The aim was to overthrow Elizabeth and put Mary Queen of Scots on the throne.

Throckmorton was eventually identified by Walsingham's spies in France and arrested. Under torture, he confessed that Mary knew about the plan from her agents in France. However, Walsingham still had no actual proof of her direct involvement.

William of Orange was the leader of the Dutch Protestants. His murder at the hands of a Catholic convinced Elizabeth's Privy Council that she could be the next target.

The Privy Council decided to draw up and sign a document called the Bond of Association. In the event of Elizabeth's murder, those who signed the Bond promised to punish not only those responsible, but also anyone who might benefit from Elizabeth's death - clearly a reference to Mary Queen of Scots.

Elizabeth's treatment of Mary Queen of Scots was only one of several reasons for the war, which had been expected for some time. In one sense, the prospect of a Spanish victory gave Mary hope, in another it made her execution more likely.

Before 1585, the threat of Mary's execution had been used to prevent Philip from launching an invasion - now that war was declared, Mary's survival was less important to all concerned.

The details of the plot were by now familiar - a Catholic rising, supported by a foreign invasion to secure Mary's release and Elizabeth's assassination.

Babington, like Throckmorton before him, was used to carry messages to and from Mary and may have been the intended assassin. The difference was that Walsingham learned early enough about this plot to be able to intercept letters exchanged between Babington and Mary (which were hidden in beer barrels) without either of them suspecting anything.

In June, Babington sent a letter to Mary telling her about the plot. Mary's reply, on 18th July, contained her approval of the plot, including plans for the murder of Elizabeth. This finally gave Walsingham the vital proof he needed of Mary's guilt. Mary's trial began on 15th October.