Christie, A: A Murder Is Announced BBC Radio 4 Full Cast Dramatisation

A BBC Radio full-cast dramatisation starring June Whitfield as Miss Marple, the deceptively mild spinster sleuth.
'A murder is announced and will take place on Friday, October 29, at Little Paddocks, at 6:30pm. Friends please accept this, the only intimation.' Nestled among the usual notices about dogs for sale and appeals for domestic help, the startling entry in the personal column of the Chipping Cleghorn Gazette has the entire village agog with curiosity. Is it a game? And who is meant to attend?
Sure enough, the evening sees a crowd of residents standing expectantly in the drawing-room at Little Paddocks. Then the clock strikes the half-hour, the lights go out, and three gunshots ring in the dark. When the lights go back on, the promised murder has been committed.
Can Miss Marple work out what has happened and why?