The Bletchley Circle and Communication Technology

  Halfway through the final episode, Susan is given a final warning to stop pursuing the case.  The deputy commissioner threatens her with consequences if he finds her at his office again and tells her that this will disappoint her husband, Timothy.  She reluctantly tells the deputy commissioner that she will stop, but once again, all the women continue to brainstorm about how they will retrieve concrete evidence against Malcolm Crowley.  If the deputy commissioner won't believe them about the postcards, they need to find his files, or other evidence, to prove he is the killer and the poor man that was arrested, Gerald Wiggins, is innocent.   Meanwhile, Susan and the other women devote their attention to the content on the postcards.  Cavendish, the old SOE director, told them that Crowley worked as an illustrator during World War II, creating provocative pictures of women to discourage foreign army men from continuing to serve the Axis powers (which primarily consisted of Germany

The third and final episode of the season opens where we left off.  Susan is in the mental hospital with Malcolm Crowley.  She does not know his true identity and he lies about who he is.  He also knows that Susan is looking for him because of the train station incident and the fact that she is directly asking for Malcolm Crowley's files.  He takes her to the file room and sits down at his desk.  He fumbles for a cigarette as he explains that he signed the Official Secrets Act of 1939, just like Susan did at Bletchley Park.  Therefore, he cannot hand over the files.  As Susan listens, she looks over at his pack of cigarettes and recognizes it is the same brand of cigarettes found at the murder sites.  She thanks him for the opportunity to talk anyway and quickly leaves the mental hospital.  Scared knowing that she was with the killer, she runs to the police to tell them about Crowley's file room.  The police respond by going to the mental hospital, but they find his office comp