It’s tough to remember a time when a plot twist like this would be surprising. Without it you’ve got piecemeal sequences from the book that don’t coalesce very well. Uta Hagen is great fun to watch, at least. 

I read the book a long time ago but I remember it being pretty decent. Not as good as Harvest Home by the same author, which I read last year & really dug. I think there’s a movie of that, too, but I haven’t seen it yet.