Greene's story begins with the premise that guilt is almost guaranteed in the murder case. There is strong eyewitness testimony that links the accused with the crime. Led by Mrs. Salmon, it is eyewitness testimony that ensures the guilt of the accused: "...no one present when the Crown counsel outlined his case believed that the man in the dock stood any chance at all." It is here in which there is a perception that the case is open and shut, all but guaranteed on a verdict of guilt.
Yet, the transformation into ambiguity from apparent certainty becomes evident in the case for the defense. The accused's twin is an element that causes Mrs. Salmon to second- guess her initial certainty. The reasonable doubt begins to creep into the other eyewitnesses, as well. Since so much of the case against the accused was contingent on the eyewitness testimony, when they begin to waffle in their commitment, the accused is free. The climax of the story when one of the brothers ends up getting hit by a bus helps to move the story into one of complete ambiguity. It becomes unclear whether the brother killed was the one accused. There is a great level of mystery surrounding the end as a result of this development.