Complex sentence: George Smiley is called by a wartime colleague, Miss Brimley, who now edits a small Christian magazine and in this position has received a letter sent by Stella Rode, a reader who claims her husband is plotting to kill her.
Split into simpler sentences: George Smiley is contacted by a wartime colleague, Miss Brimley, who now edits a small Christian magazine. She tells Smiley that she has received a letter from a subscriber, Stella Rode, claiming that her husband is plotting to kill her.