Redefining conspiracy

I was thinking about the whole conspiracy angle and although I feel I know what It means I checked out some definitions. Here is one.

A secret agreement between two or more people to perform an unlawful act a plot to carry out some harmful or illegal act (especially a political plot) a group of conspirators banded together to achieve some harmful or illegal purpose.

Then as I thought about it some more, I realized that it’s not really a truthful definition. Who is to say that there is not only “one person” conspiring and all the people he/she comes in to contact with are fully unaware of the conspirational plans. Yet at the same time they fit perfectly in to his/her conspiracy without knowing it, wouldn’t this be the ultimate conspiracy? What do you think? Is it possible and can you think of any historic example that could make it possible?