I think you need this set up:
Playouts containe one or more scenes
Stories contain more than one scene.
This would appear to be a many to many relationship:
Stories::__pkStoryID = Scenes::_fkStoryID
Playouts::__pkPlayoutID = Scenes::_fkPlayoutID
See this link if the above notation is unfamiliar: Common Forum Relationship and Field Notations Explained
With such a structure a portal to Scenes on the Stories layout would list all scenes records contained in that story and a portal to scenes on the Playouts layout would list all scenes portrayed in that playout.
And this calculation from playouts would produce your comma separated list of scenes for a given Playout record:
Substitute ( List ( Scenes::__pkSceneID ) ; ¶ ; ", " )
still trying to find time to have a go at this, but thanks. will let you know how I go.