So I assume you want to start the narrator when a level starts? There is a hack where you can do this: place your hero right in front of an invisible actor, and when the game starts the screenplay will be triggered.
But you also seem to want it at other moments. So when do you want that to be triggered? When the hero walks over some space? Or after a timeout?
Do you know of some game that already does this, so I can take a look?
A lot of questions, I know ;).