What does Aunt Ada Doom keep talking about and what's your "take" on this?

Aunt Ada Doom's rambling thoughts keep going back to an event she witnessed in a shed, a mystery which, like the wrong done to Robert Poste, teases the reader but is never revealed. The madness from this event is the tool Aunt Ada uses to dominate and control her family, claiming she will go madder if any of them leave. Through her voice it is clear that the madness has certain advantages and is thus pretentious.