coup de théâtre

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 coup de théâtre that would have been spoiled if he had come from there in the first place.

I had arranged to track her husband down, reason with him, work on his feelings, telegraph for his wife, and in an affecting interview throw them into each other's arms. Now, goodness knows what would happen. Certainly not my beautifully conceived coup de theatre.