In the movie, the story takes place on a train. The train is small and always moving, which makes Holmes face many challenges when investigating the case. On the train, Holmes needs to find clues in a limited space and face various obstacles from different passengers. There is a scene in the movie where Holmes chases the suspect between train cars. Such a tense chase makes the audience feel a sense of oppression.
The film shows the development of the case from Holmes' perspective, and the audience also follows his reasoning process to uncover the truth step by step. Through this perspective, the audience can clearly see how Holmes observes details and analyzes clues. Because the train is a closed environment, all the secrets are hidden in a limited space, and Holmes' reasoning becomes more important.