While this certainly fits in the GIC area, it sounds like you've already got a set plot in place. Group RP's can of course be guided, but I think you'll find that people will often try to do their own thing. You may see the plot attempt to change in ways you perhaps did not expect, even if it still moves towards what you had originally planned. Essentially, you can give the setting and some major characters, but there is little guarantee exactly [i]how[/i] the story progresses.