The prisoners of war at Chicago, Illinois, being released, and the great conspiracy in the North once fairly inaugurated, the capture of the steamer Michigan was to be one of the combined movements that were to startle the country, and aid the conspiracy in overturning the authority of the United States Government, With the "Michigan" in their hands, the conspirators would have a powerful auxilliary in their pernicious designs upon the country, and be able to render effective aid to the Southern Rebellion; ruining the commercial status of the United States on the great lakes, and effectually closing all the ports on their borders, and in addition to this, their laying all the large towns and cities on the northern portion under contributions, and exacting from them enormous sums of money, through fear of bombardment. The plan of the conspirators to get possession of the Michigan was by bribery and by surprise. Mr. Thompson, in his efforts to seize the vessel, secured the services of a man named Cole, of Sandusky City, who, whilom, had been a citizen of Virginia, but who still retained his sympathies for the rebellion, and took an active part in aiding it whenever he had an opportunity, and a woman, said to have been his paramour, who carried dispatches backwards and forwards between the parties. This man Cole seems to have been the most wiley conspirator of them all, and played his infamous part of the plot with the most adroit shrewdness; and the defeat of the whole scheme was not owing to any blunder of his, but rather the blunder of those who employed and furnished him with the means. Having been well supplied with money by Mr. Thompson, and no limit put to his expenses, he began his work with a will. He seems to have begun by getting generally well acquainted with the officers of the vessel, by feasting them, and now and then lending them money, or accommodating them in some other way, until he had won the confidence of all those in command of the steamer, as well as those in charge of Johnston's Island. After a time, he found out those who were most vulnerable on the money question, and those whom he did not dare to approach upon the subject. Of the latter class, there is one mentioned in particular by the rebels, whose suspicions they did not care to arouse, and which they made every attempt to lull. This was an officer named Eddy, from Massachusetts. Of the former class, whom they bribed, the rebels mentioned particularly the chief engineer, who, they said, had agreed, for twenty thousand dollars in gold, to get the machinery out of order, and otherwise aid in the vessel's capture, and one or two others. [Illustration: BRIG. GEN. CHARLES WALSH,