Watch Ingrid Bergman, there's a reason why she won the Oscar. Watch her eyes when she can't hold back her fear of being caught when she's first questioned. Everyone does an excellent job here. Some may think Lauren overdoes it and that's not so - watch her final scene when she's calm and quietly talking - earlier she purposely overacted because her character was acting a part. Sean and Vanessa make a red hot couple - it's sad not seeing more of them together.
25: Hercule declines to protect Richard Widmark. Richard thinks someone's going to kill him. The birth of something new.
45: Richard's death is examined by the doctor, Hercule and his friend. We become aware of a number of things: we learn that the stab wounds are different, that there are "Too many clues in this room." Soon they discover the identity of Richard Widmark's character and his connection to the Daisy Armstrong kidnapping; it is believed that he is responsible for 5 deaths. Now that I'm aware.
60: Hercule is told that the inquiry must end before the train leaves the snow. Lauren Bacall found a button, later it is learned the button is not missing. Hercule thanks Ms. Bacall for playing her part. The identity of a handkerchief is in question. There's no going back now.
-45: Sean Connery is questioned. Hercule discovers that the Royal Scots connects Sean to the Armstrong kidnapping. Discovery.
-25: We learn Jacqueline Bisset, who plays the late Daisy Armstrong's sister, is on the train. We learn the princess owns the mysterious handkerchief. We learn the cook in the Armstrong house is on the train. Eventually, we learn that 12 people on the train have reason to want Richard Widmark's character dead. The evidence keeps escalating as Albert Finney plays the final monologue like nobody else could. Somehow he makes it plausible, inevitable, acceptable. The final turning point.