"There’s a plot in this country to enslave every man, woman, and child. Before I leave this high and noble office, I intend to expose this plot.”
There's no record of it. I'm not sure if it was misattributed to him or simply fabricated. He did however address such things:
"The very word "secrecy" is repugnant in a free and open society; and we are as a people inherently and historically opposed to secret societies, to secret oaths and to secret proceedings..."