Gunpowder Plot, conspiracy to kill James I, king of England, as well as the Lords and the Commons at the opening of Parliament on November 5, 1605. The plot was formed by a group of prominent Roman Catholics in retaliation against the oppressive anti-Catholic laws being applied by James I. The originator of the scheme was Robert Catesby, a country gentleman of Warwickshire. First he took his cousin Thomas Winter and his friends Thomas Percy and John Wright into his confidence, along with Guy Fawkes, a soldier of fortune. They in turn drew other Roman Catholic gentlemen into the plot, among them Sir Everard Digby, John Grant, Ambrose Rokewood, Francis Tresham, Thomas Winter's brother Robert, and John Wright's brother Christopher. The conspirators discovered a vault directly beneath the House of Lords. They rented this cellar and stored in it 36 barrels of gunpowder.

In the final arrangement, Fawkes was to set fire to the gunpowder in the cellar on November 5 and then flee to Flanders. Through a letter of warning written by Tresham to a peer, the plot was exposed. Fawkes was arrested early on November 5 as he emerged from the cellar. Fuses were found concealed on his person, and in the cellar a lighted lantern and the barrels of gunpowder were discovered. Examined under torture on the rack, Fawkes confessed his own guilt and after long obstinacy revealed the names of his associates, nearly all of whom were killed on being taken or were hanged along with Fawkes on January 31, 1606. The Gunpowder Plot is commemorated annually in the United Kingdom on November 5; on this day it is the custom to burn Guy Fawkes in a ragged effigy. The slang word guy is derived from these effigies.