Doing Agatha (2008)

An actress famous for her performances in Agatha Christie plays loses her mind and disappears shortly before she is to open on Broadway in a revival of The Mousetrap. Meanwhile, at a struggling community theater in Bedlam, Connecticut, a woman walks in on a rehearsal of The Unexpected Guest. The female lead has just quit the cast, mere days before opening night; but luckily, this stranger knows the lines and agrees to take the role. What seems like a stroke of luck unravels on Opening Night, as the murder mystery morphs into an Actor's Nightmare.