The government appeared sceptical about the letter and Salisbury seemed to treat it very coolly. However, it is likely he did not want to scare the plotters into premature flight.
On the evening of 4 November a royal official, Sir Thomas Knyvett, and Edward Doubleday found Guy Fawkes, who was using the alias John Johnson, and his gunpowder.
An entry from the Journal of the House of Commons which is held by the Parliamentary Archives records what happened when the House briefly assembled on the morning following the arrest of Guy Fawkes. The Clerk of the time, Ralph Ewens, added a note about the discovery of the plot:
This last Night the Upper House of Parliament was searched by Sir Tho. Knevett; and one Johnson, Servant to Mr.Thomas Percye, was there apprehended; who had placed Thirty-six Barrels of Gunpowder in the Vault under the House, with a Purpose to blow King, and the whole Company, when they should there assemble. Afterwards divers other Gentlemen were discovered to be of the Plot.
On the morning of 5 November when they realised that the plot had been discovered, most of the conspirators fled to the Midlands. As details emerged, the government issued a series of proclamations ordering their arrest.
Uprising melts away
Catesby persuaded his companions to continue with the second part of the plan: to try to rally Catholics in England and Wales to join in an uprising against the government. They stole horses from Warwick Castle but no more than fifty people joined them and these soon melted away.
The authorities caught up with the conspirators on the morning of Friday 8 November at Holbeach House near Kingswinford, in Staffordshire. Several, including Catesby, had already been injured in an accident trying to dry out their water-soaked gunpowder.
There was a brief shoot-out: Catesby, Thomas Percy, Christopher and Jack Wright were killed. Thomas Winter and Ambrose Rookwood were captured and brought to London.
Sir Everard Digby, Thomas Bates, Robert Keyes and Francis Tresham were arrested over the next few days, whilst many others were seized under suspicion of involvement. Robert Winter evaded arrest until January 1606.
On Saturday 9 November Parliament assembled to hear a speech from the King describing what was then known about the plot. The speech was later published as a pamphlet at the end of November as 'The King's Book'.