Disappointed by the failure of James I’s peace treaty negotiations with Spain to improve their position, a handful of young Catholic gentlemen from the Midlands, some of whom had been involved in previous plotting, decided to take action.
At their centre was the charismatic Warwickshire gentleman Robert Catesby. In May 1604 he proposed a plan to blow up the King, together with the House of Lords and the House of Commons during the ceremonial opening of Parliament.
The family links of fellow plotter, Thomas Percy, to the powerful Earl of Northumberland, for whom he worked as steward, would help the conspirators gain access to Parliament.
After the explosion the plotters hoped to gather together the Catholic gentry of the Midlands and seize Princess Elizabeth, the only one of King James' children who would not be at the ceremony. What would happen next was never properly worked out.
A small group of Catholic priests, including Henry Garnett, the head of the Jesuit mission to England, did have some knowledge of what was being discussed, and tried to discourage it. Garnett and his fellow priests did not, however, pass on what they knew to the Government.
The plotters initially rented a house on one side of the House of Lords and tried to dig a tunnel in which they could plant gunpowder; however this proved too difficult a task.
In March 1605 they managed instead to rent a basement undercroft - often referred to as a cellar - directly underneath the House of Lords.
After a series of postponements Parliament's opening was finally set for 5 November 1605. By then 36 barrels of gunpowder were in place in the storeroom, under the watchful eye of Guy Fawkes.