One of the conspiracies of that season, when the air was alive with the rumours of conspiracy, was a genuine plot and a murderous plot, and therefore deserves an especial notice. This was the Cato Street Conspiracy, as it was called, a name of fear to many succeeding generations. For no short space of time a mere allusion to the Cato Street conspiracy was believed by honest Tories to be quite enough to damp the enthusiasm of the most innocent reformer. The agitation in favour of important changes in the system of government had greatly fallen off for a while. Nothing seemed to be coming of the movement; the followers grew dissatisfied, and blamed their leaders for their supposed lack of activity; despondency and disappointment were abroad among the ranks; the funds ceased to come in; and the whole organisation seemed for the moment likely to collapse. It was just then - in 1819 - that the massacre of Peterloo, as it was called, and the subsequent action of the Government in reference to it, interposed to give a new stimulus to popular agitation, and to fan again into a burning flame the smouldering embers of popular passion. One of the indirect results of the Government's ill-advised action was the Cato Street Conspiracy.
The conspiracy, with all its horrors, was a small affair in itself, confined to a very limited number of conspirators, and, until its actual outbreak, as completely unknown to the vast majority of the reform agitators as it was to the vast majority of the general and unconcerned public. Indeed, it is by no means certain that there would have been any Cato Street Conspiracy at all but for the working of the abominable spy system, which was undoubtedly abetted by the officials of the Home Office. The first information of the existence of any such conspiracy was given to the Home Office by a man named Edwards, who kept a small shop at Eton. Edwards professed to have discovered a desperate plot for the assassination of the King's Ministers, and indeed it may be assumed of the King himself. The story was naturally told at once to Lord Sidmouth, the Home Secretary; and Edwards was promptly taken into the pay of the Home Office. Whether Edwards actually started the conspiracy itself it would now be impossible to say; but it is certain that he and other agents of a similar character did go about London and the country, wherever they found discontented men, and whisper to them of a tremendous plot to wreak a just vengeance on the King's Ministers and to form a starting-point for a great popular revolution. Very few men indeed were foolish enough to be persuaded to join this preposterous conspiracy; but it had from the beginning, or at all events it had after the sedulous efforts of the Government spies, the leadership of a man named Thistlewood, the very sort of man whom Fate and his own fault had marked out for such a part. Thistlewood was just a type of the creature who is found during the progress of all great popular movements, who belongs to the dregs of the agitation, and is by the hand of Nature quoted and signed to mix himself up in deeds of blood. Perhaps he was rather a crazy fanatic than an ordinary assassin; but it is certain that a spirit of private vengeance and hate urged him in his later days, much more than any desire, however wild and incoherent, for the emancipation of any downtrodden class. He had been concerned in other agitations, and had been put on his trial in one instance and acquitted. Perhaps if he had not been crazy, he might have been contented with the result; but he instantly blossomed forth into that most dangerous growth, a man with a grievance.
He took the extraordinary course of sending a challenge to Lord Sidmouth. Perhaps Lord Sidmouth might have done well if he had taken no notice whatever of the challenge; but of course there are laws for the protection of the Ministers of the Crown from invitations to single combat, and Thistlewood's mock heroic performance was punished by a year's imprisonment. When his time of incarceration was over, he came out a thoroughly desperate man. He got a few creatures about him, as ignorant and as desperate as himself, and he initiated them into his plot, which was to murder the Ministers, seize on the Bank, the Mansion House, and the Tower of London, and forthwith set up a provisional government. One of the wild fantasies among the discontented desperadoes of that time was the notion that by capturing the Bank and the Mansion House and the Tower of London they could establish a secure basis for the construction of a new system of government on the principle of "down with everything." It seems hard to think now that even men like Thistle-wood and his little gang of conspirators could have believed for a moment in the possibility of such a scheme; but Thistlewood and some of his associates undoubtedly did believe in it, and they were for going to work at once, and beginning with the assassination. Some delays, however, intervened, amongst others the delay caused by the death of the King and the Duke of Kent and the uncertainty as to whether the accession of George IV. might not rid the country of the old Tory Ministers whom they hated. After a while the course of events furnished them with an opportunity which seemed to be sent by Fate for their very purpose. The man Edwards, the spy in the pay of the Home Office, obtained information for them that there was to be a Cabinet dinner on the next day at the house of Lord Harrowby. There, then, was the whole murder made easy. Some of the conspirators were to watch round Lord Harrowby's house; one was to knock at the door and send in a note while the statesmen were at dinner, and then the conspirators were to rush in a body through the open door and to massacre their enemies. So elaborate and so comically dramatic were their preparations, that some of the conspirators, it seems, came provided with bags in which to carry away the heads of Lord Sidmouth and Lord Castle-reagh, the two men especially hated by Thistlewood and most of his friends.