Arrest, trial and pardon
Soon after midnight on 1 January 1691 Preston, Major Edmund Elliott, and John Ashton were seized as they lay concealed in the hatches of a smack making for Calais or Dunkirk. A packet of treasonable papers, tied together and weighted in order to be sunk in case of surprise, was dropped by Preston with his official seals, and seized upon the person of Ashton, who had tried to conceal it. The prisoners vainly attempted to bribe their captors. On 3 January Preston was sent to the Tower, and on the 16th was indicted at the Old Bailey in the name of Sir Richard Graham for high treason. He pleaded that as a peer of England he was not within the jurisdiction of the court, but this plea being overruled, he was on 17 January found guilty, and condemned to death two days afterwards. His estate and title of baronet were forfeited to the crown. Some months passed before his fate was decided. Lady Preston, on petitioning the queen for her husband's life, received an intimation that he could save himself by making a full discovery of the plot. During some time he regularly wrote, it is said, a confession every forenoon, and burned it every night when he had dined. At last he confessed his guilt, and named Clarendon, Dartmouth, Francis Turner, Bishop of Ely, and William Penn as his accomplices. He added a long list of persons against whom he could not himself give evidence, but who, if he could trust to Penn's assurances, were friendly to King James. After several respites, the government, convinced that he could tell even more, again fixed a day for his execution. At length, on 1 May, he made a further confession, and gained thereby another reprieve of three weeks, 'which, 'tis believed,' writes Luttrell, 'will end in a pardon'. A patent was passed for his pardon soon afterwards, and on 13 June he obtained his release. His estate was, however, still retained by the crown as security for his good behaviour, a supposed equivalent being granted him from the exchequer. Subsequently, in September 1693, Queen Mary II granted £600 a year from the forfeited estate to Lady Preston and her children. The attainder could not affect his Scottish peerage, as no act of forfeiture against him passed in Scotland. Early in August 1691, Preston was recommitted to Newgate Prison for refusing to give evidence against some 'criminals,' but was soon bailed out. Thereafter he was permitted to retire to Nunnington Hall in Yorkshire, which he had inherited from his great-uncle, pursued by the execrations of his party.