I don't know how to multi quote so I'll just do it this way
Cherry91 - thanks! It's been a while since I've seen that movie so I may have forgotten the details. I did think the movie implied that he has been romantically involved with his sister, but maybe not. Still, as you describe it, #1 does not happen at all in the book, and #2, while closer to the truth, is not far enough -- there is actual murder, and she does die. Also the abortion plot of the movie was not at all in the book -- it seems out of place for the time period, and is pointless to add because it has no connection to the real plot! If anything, I felt that it cheapened and overshadowed the actual plot, which is twisted and powerful enough!
Re: Agatha Christie's racism. Sadly, I have to agree. I enjoy the plots of her books but could do without the random casual racist references. I'm Jewish, so I probably notice this most with Jewish characters -- they are always caricatured in a negative light, not full fleshed characters. They always have a hook nose, sallow color, are stingy with their money, and are "foreign" and "don't belong". She throws in anti-Jewish references even when they have no real relation to the plot, just as background color. Not to mention her liberal use of the N-word, even by supposedly intelligent and enlightened characters. I could definitely do without all that!