Murder on the Orient Express discussion

I would have to read it again to remember the specifics, but once the plot was revealed, it was clear to me that everyone knew perfectly who everyone else was, they had planned to be there and to do what they did, and that they all pretended not to know each other or who the others were (in the context of their common story).

Yes, they all know who each other are and what the plan is. The Countess is innocent in that she didn't take part but she did know about what was happening.