I was watching Murder Under Glass over the weekend, and it shows Paul Gerard preparing the Fugu poison before his dinner with Rossi. From what I can tell, Rossi hasn't yet told Gerard that he plans to end his blackmail and expose and ruin him. Why then, would Gerard have reason to prepare the poison before he is told? Something had to have happened before the opening scene of this episode to tip Gerard off and set his plan of murder into play. Something we aren't shown.
What other episodes have a "scene before the opening scene"?
I always thought Grace Wheeler sneaking extra pills to knock out her husband was basically her murder plan already set in motion, even BEFORE she got the "no" answer from her husband on funding her show. Cold.