The movie skips around, and we go from present to past. Switching back and forth helps viewers understand the characters better. It helps to build on the mystery of the film. We see that perhaps Megan and Scott aren’t that perfect a couple. The flashbacks allow us to see what Rachel and Tom’s life was like when they were together. The flashbacks help Rachel solve Megan’s murder. The three female leads, Rachel, Anna, and Megan, are the narratornarrators for the film. For example, we know that Megan is dead before she herself knows, since Rachel talks about the investigation. From Anna's point of view, we see why she doesn’t like Rachel. One time, Rachel attempted to take her and Tom’s baby girl. The fact they don't like each other creates a bunch of drama.