A crack in the mirror - Agatha Christie

The famous actress, Marina Gregg, witnessed a murder in her country house called Gossington Hall.

But what did she see just before the accident? What caused a look of immobility and horror to appear on her face, which no one else had seen but Mrs. Dooley Pantry?

Of course, Dolly knows the only person who can explain it: her old friend; Miss Marple…