Everyone has a pre-determined role. There isn't necessarily a defined dialogue, but the jist of what you say and do IS pre-determined. For example:
A very experienced couple we know from an S&M club in NYC that is always playing on the edge, had planned a consensual non-consensuality scene. That means the submissive consents to anything, including things they would NOT consent to if they knew they would take place. The submissive has no idea of what they are consenting to and has no right or ability to end the scene for any reason--no safe word. So, a few years ago the wife wanted to do a non-consensual scene, the details of which she was never to know. About five years ago her husband and my husband and I, hooded and kidnapped his wife in the middle of the night (she didn't know it was us). We drove around for an hour or so and brought them to our house for the scene, which was mostly one of bondage and sexual torment. We took many liberties with her body for almost 24 hours before she was brought back to her house, still hooded and finally released. When her husband told her that she had just experienced the non-consensuality scene they had planned more than a year earlier, she said she would NEVER do that again because she was absolutely terrified, felt powerless and feared for her life.
I don't want to get into too many details, but I will say it was the most daring, exciting scene I had ever done with another couple. I know I would have been terrified out of my wits if I was kidnapped, and she was too. She was under severe stress and at times put on a real struggle and cried a lot. I have to say, at times I felt sorry for her, but we had agreed to help with the scene.
Luckily, we are still friends today but we don't look back on this with good feelings. There are limits, even for players on the edge, and this went beyond them.