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 negotiate an Anglo-Spanish treaty. Tassis quickly realised that any chance of a successful Catholic rebellion was unlikely, and discounted Thomas's claim that, with funding, "3,000 Catholics" would be available for the cause. After meeting with King James he wrote to Spain emphasising the need to prioritise peace with England over the freedom of her Catholics. According to contemporary accounts late in February 1604 Thomas's cousin, Robert Catesby, invited him to his house in Lambeth, but Thomas was indisposed and could not attend. Catesby sent a second letter that Thomas did respond to, and when he arrived he found his cousin