Robert and Thomas Wintour is written about the Gunpowder Plot is derived from Thomas's confession, signed on 23 November 1605; details of the so-called Spanish Treason were added three days later. One of only two confessions printed in the "King's Book" (a highly partial contemporary account of the affair), Thomas Wintour's was the only account the government had of a plotter who had been involved from the beginning; Guy Fawkes, weakened by days of torture, may have been at the heart of the group, but he was not at its first meetings. However, Antonia Fraser views the document with suspicion, not least because Thomas's
Robert and Thomas Wintour would nott answere". With the addition to the conspiracy of Thomas Percy (John Wright's brother-in-law), the five plotters met at the Duck and Drake inn, in the fashionable Strand district of London, on 20 May 1604. From hereon Thomas Wintour remained at the heart of the conspiracy. The group leased properties in London, one in Lambeth for storing the gunpowder that was rowed across the Thames to its destination. His confession has the plotters digging a tunnel toward their target during one of the several prorogations of Parliament, abandoned when the chamber directly beneath the House of Lords became available.