"The plot was discovered, in the official version, [on Saturday 26 October] through a mysterious anonymous letter to Lord Monteagle [William Parker], a Catholic, warning him not to attend the State Opening. Whether the letter was genuine, from a fellow Catholic concerned about Monteagle's welfare, or whether it was a forgery and sent from within government circles, is uncertain."
"In any event, on the 4th of November an initial search was made by Lord Monteagle
and the Lord Chamberlain, Lord Suffolk. They discovered
My lord out of the love i beare to some of youere frends i have a caer of youer preseruacion therfor i would advyse yowe as yowe tender youer lyf to devys some excuse to shift of youer attendance at this parleament for god and man hath concurred to punishe the wickednes of this tyme and think not slightlye of this advertisment but retyre youre self into youre contri wheare yowe may expect the event in safti for thowghe theare be no appearance of anni stir yet i saye they shall receyve a terrible blowe this parleament and yet they shall not seie who hurts them this cowncel is not to be contemned because it may do yowe good and can do yowe no harme for the dangere is passed as soon as yowe have burnt the letter and i hope god will give yowe the grace to mak good use of it to whose holy proteccion i comend yowe.
[Guy] Fawkes and the wood and
[the other ringleader] had provided to cover the kegs of powder. Sir Thomas Knyvett, a retainer
of the Court, and Justice for Westminster, then searched the cellar thoroughly with a group of men at midnight, found the gunpowder, and arrested Fawkes.
It is not clear why the government waited nine days to act on the warning. But nevermind. The plot had been thwarted. The King and the kingdom had been saved. All that remained was to 'bring the evildoers to justice'.