SANDWICH, June 6,1862.

JAMES GORDON BENNETT,Esq.,New York City.

SIR: The contents of this letter I wish you would forward to the Secretary of War if you think best. There is a scheme on foot here and on the other side of the river between some Southern sympathisers and Marylanders to liberate the rebel prisoners On Johnson's Island. They have agreed upon a plan at last. Their first plan was to charter a steam craft, and the boat was actually fitted up for the purpose as far as running was concerned, she not having been in commission for some years. This plan was, however, abandoned on account of its being necessary to let the crew in the secret and for the large expense the loss of the boat would entail upon the party, besides implicating the owner.
Attention would be drawn more to a steamer entering the bay than a sail vessel, etc

  Their plan now is to purchase an old sail-vessel which one of their party is to own and which he is to say was stolen. This vessel is to be placed at some point in or near the River Detroit. One of the party disguised is to engage a powerful tug to go for this vessel so as to arrive alongside after dark when a party from the vessel are to board the tug, make prisoners of the crew, take charge, tow the vessel to Sandusky Bay, surprise the guard, liberate the prisoners, who are to be informed beforehand if possible, place them on the vessel, tow her to Canada where they will be landed. This vessel will then be set adrift, the tugs crew liberated and the tug given up to them again. This plan will be carried out as soon as things can be gotten in readiness.
   

     CANADIAN.

N.B.-For strong prudential reasons I must use a nom de plume. I will, however, call at the Herald office in autumn, when my business will take me to New York. This will be mailed at Detroit or Niagara Falls