I see no reason why the gunpowder treason should ever be forgot

The first active step (24 May, 1604) was to hire as a lodging Mr. Whynniard's tenement, which lay close to the House of Parliament, and had a garden that stretched down towards the Thames. But no sooner was this taken than a government committee claimed the right of sitting there, so the preparations for mining had to be postponed for six months. Before Christmas, however, they had opened a mine from the ground floor of their house, and advanced as far as the wall of the House of Lords; then they made slow progress in working their way through its medieval masonry. In March, however, they discovered that the cellar of the House of Lords might be hired, and on Lady Day, 1605, a bargain was struck for that purpose. They had now only to carry in their powder, and cover it with faggots of firewood, and the first part of their task had been accomplished with surprising facility. They then separated, to make preparations for what should follow when the blow was struck. For this it was necessary to procure more money, and by consequence to admit more members. Five were mentioned before, and five more, Christopher Wright, Robert Keyes, Thomas Bates, Robert Winter, and John Grant had been added since. Three richer men were now sworn in, Ambrose Rookwood, Sir Everard Digby, and lastly, Francis Tresham. It was this thirteenth man who has been generally believed to have caused the detection of the plot, by a letter sent to his cousin Lord Monteagle on 26 October. This mysterious document, which is still extant, is written in a feigned hand, with an affectation if illiterateness and in the obscurest of styles. The recipient was warned against attending Parliament on the day appointed, and hints were added as to the specific character of a "terrible blow" that would befall it. "There [will] be no appearance of any stir"; "they shall not see who hurt them"; "the danger will be past as soon as you have burnt this letter." Monteagle, having received this letter, first caused it to be read aloud at his table before some mutual friends of the conspirators, then he took it to the government. more here and here