I think you need to restructure here.
Link by StoryID to a join table that in turn links via a TalentID field to your Talent key.
Put a "Role" field in the join table to identify the role for that particular person in that particular episode.
From the Epsiodes record, you wouldn't want to see the same TalentID value appear more than once.
From a calcuation standpoint, you could use this auto-enter calculation in a field in Story_Talent:
Episodes::EpisodeID & " " & TalentID
A unique values validation rule on this field would then catch instances where the same Talent record is selected more than once for the same Episode.
ahh, I could create them automatically when I make a new story (with a cascading delete option) and the user would never have to know it existed.
Do you mean a diminishing value list? I don't think a cascading delete would be a good idea.