Sentence:  This may be due to the fact that Aeschylus, in the last play of the "Oresteia" (458 B.C.), brings him to Athens to stand trial for his mother's murder--a <WSD>coup de théâtre</WSD> that would have been spoiled if he had come from there in the first place. 
Meaning of the word marked with <WSD> tags:  A sudden or unexpected event in a play, pulled off by the author, the director, or even an actor.