Other movies with a similar plot? [*SPOILER*]
It's a powerful plot. X and Y have a guilty conscience about a past crime that they've managed to keep under wraps for some years, and react anxiously at the unexpected arrival of Z, whom they suspect of knowing of their crime and of having an ulterior motive by turning up on the scene, when in fact Z is blissfully unaware of it. X and Y's guilty conscience and defensive behavior end up exposing their crime to Z.
Off the cuff I can think of one other movie with a similar plot, viz., Bad Day at Black Rock. Any others come to mind?