Percy helped fund the group and secured the leases to certain properties in London, one of which was the undercroft directly beneath the House of Lords, in which the gunpowder was finally placed.

When the plot was exposed early on 5 November 1605, Percy immediately fled to the Midlands, catching up with some of the other conspirators en route to Dunchurch in Warwickshire.

[5] I understand by this bearer, my servant Meyricke of your willing disposition to favour Thomas Percy, a near kinsman to my brother of Northumberland, who is in trouble for some offence imputed unto him.

Despite not being a close relative, in 1595 the 9th Earl of Northumberland made Thomas responsible for collecting rents from his northern estates, and the following year appointed him constable of Alnwick Castle.

[3][4] Thomas exercised his authority in a manner which gave some cause for complaint, not least from an officer he replaced,[11] and contemporary reports of his dealings with the earl's tenants include claims of mismanagement and bribery.

[nb 2] During a border skirmish he killed James Burne, a Scot, for which he was imprisoned at a London gaol, but his release was secured by the intervention of Robert Devereux, 2nd Earl of Essex.

Thomas subsequently aided Essex in a conspiracy against the Scottish warden of the middle marches,[5] although unlike several others who later joined the Gunpowder Plot, he was not a member of the earl's failed rebellion of 1601.

[5][11] Henry Percy was considered a supporter of the Catholic cause, and on several occasions before 1603, suspecting that Queen Elizabeth I did not have long to live, he entrusted Thomas with the delivery of secret correspondence to and from her probable successor, King James VI of Scotland.

Northumberland's uncle had been executed for his involvement in the Rising of the North, a plot to replace Elizabeth with James's mother, Mary, Queen of Scots.

Almost a year earlier, he had called at Robert Catesby's home at Ashby St Ledgers, and complained bitterly about James, who since succeeding Elizabeth had done little to fulfil his expectations.

"[24] Thus Percy found himself at the Duck and Drake inn near the Strand in London, along with Catesby and his cousin Thomas Wintour, John Wright and Guy Fawkes.

[22] While the plotters did not then have a detailed plan, Percy's appointment on 9 June as a Gentleman Pensioner gave him a reason to establish a London base.

The fate of Elizabeth's brother, Henry, was uncertain; although the plotters presumed that he would die with his father, they decided that, if he did not attend Parliament, Percy should kidnap him.

[nb 5] James felt that it hinted at "some strategem of fire and powder",[40] perhaps an explosion exceeding in violence the one that had killed his father, Lord Darnley, in 1567.

[5] The celebrated astrologer Simon Forman was employed to divine his whereabouts, a rider was sent to look for him in northern England,[45] and a search was made of Essex House.

[46] A relative of Lieutenant of the Tower of London William Waad encountered Percy leaving London, which led to Waad writing the following letter to Salisbury on 5 November: It may please your good lordship my cousin Sir Edward York, being lately come out of the north and coming this afternoon to me, upon speech of the happy discovery of this most monstrous plot, he telleth me he met Thomas Percy, the party sought for, going down to the north disguised [...] From the Tower in haste.

[47]Accompanied by some of his fellow conspirators, Percy's flight ended at about 10:00 pm on 7 November, at Holbeche House on the Staffordshire county boundary.

[48] News of the battle soon reached London, rendering superfluous a government proclamation made on the same day and which offered a rich reward for his capture.

[49] The survivors were taken into custody and the dead buried near Holbeche, but on the orders of the Earl of Northampton, the bodies of Percy and Catesby were exhumed[50] and their heads displayed on spikes at "the side of the Parliament House".

His failure to ensure that Thomas took the Oath of Supremacy upon his appointment as a gentleman pensioner,[53] and their meeting on 4 November, constituted damning evidence,[54] and the Privy Council also suspected that had the plot succeeded, he would have been Elizabeth's protector.