The science fiction content of Scientology is revealed to them after they have reached the state they call "Clear", meaning freed from the aberrations of the mind. However, perhaps "brainwashed" would be a more applicable word to describe the mental state of someone who has survived the near entire delusional contents of their subconscious mind brought to the surface and presented to them as "truth".
On the "advanced" levels (called OT levels) above the state of "Clear" they encounter the story of Xenu. Xenu was supposed to have gathered up all the overpopulation in this sector of the galaxy, brought them to Earth and then exterminated them using hydrogen bombs. The souls of these murdered people are then supposed to infest the body of everyone. They are called "body thetans". On the advanced levels of Scientology a person "audits out" these body thetans telepathically by getting them to re-experience their being exterminated by hydrogen bombs. So people on these levels assume all their bad thoughts and faulty memories are due to these body thetans infesting every part of their body and influencing them mentally. Many Scientologists go raving mad at this point if they have not done so already.
Actually achieving the state of clear means that they have cleared out your bank account.
Don't forget the part about humans evolving from clams... Seriously, everyone should check out xenu.net; it's hilarious and informative.
Well, doggoneit, so that's the problem I'm having. Whenever I try channelling JP Morgan for financial advise, all I get is that voice telling me to nuke City Bank. It's interference from Xenu.
(Now, did I place that nuclear trigger in the laundry basket or litter box?)