I am sitting surrounded by pages of printed screenplay.
The opening act is sitting in one pile. That is fairly tight already. I may need to back-write some details into it to justify what happens later, and I will need to work on the dialogue, of course. But the scene by scene structure is more-or-less in place.
Similarly, Act 3 is sitting in a pile. The details of what happens may change. But the basic structure is fairly well established.
Placed in a long line on the floor are the pages of Act 2. This is the area of the script where most of the changes are going to have to happen. This is still fluid. With it laid out like on the floor, I can see in one glance where the long and short scenes lie. I can spot patterns and rhythms.
What I have found today are three significant sub-plots which can be developed. These will break up the rhythm of the main story and make it feel less linear. There is a character who has already died at the beginning of the movie. Her story can be developed as can the investigation into her death. There is also a power struggle going on between two of the secondary characters. This is going to be opened up. And finally, I need an excuse for one of the convict characters to start a fire in her cell. I'm not sure what that is going to be yet, but I know how they put it out!
I also watched the original movie again, trying to get the voice of the central character, Ellen Carter. I haven't quite got it pinned yet, but I'm not far off. Her main characteristic is that she doesn't say too much. She looks at people and they tend to say things to her.