The doctor was acquitted, but not liberated, for a charge of great magnitude was suspended over his head, which, at length, descended in the form of an accusation for high-treason. The government had received information of a formidable and dangerous conspiracy, in which Dr. Watson and others were stated to be deeply implicated, and the parties were in consequence apprehended, and with the doctor were committed to the Tower. A bill being found by the grand jury, Watson, Thistlewood, Preston, and Hooper, were brought up from the Tower to the court of King's Bench, on the 17th May 1817. They severally pleaded not guilty, and were then taken back to the Tower, from which they were again brought up on the 9th June. Dr. Watson was first arraigned, and John Castles was the witness called to prove the most material facts against him. He said that he knew the prisoner, and had not had any promise of pardon for giving evidence. He became acquainted with the prisoner about a month before the Spafields meeting, and saw him at the Cock in Grafton-street, where he went to meet a society called the Spenceans. On the following night he met Watson and Preston by appointment at the Mulberry Arms, Moorfields, at a society of the same description; and he there saw present young Watson, Hooper, Thistlewood, the two Evanses, father and son, and one John Harrison. After the meeting broke up, he walked away with the elder Watson, who observed, that it was a very easy matter to upset government, provided a few good fellows would act together. He then said, that he had drawn out a plan that would debar the cavalry from acting, by interrupting the horses, and that he had got several people who had solicited at different houses, and that they had formed a committee which was sitting, to devise the best modes and plans. He inquired where the witness lived, and promised to call the next morning, and show him the plan.