Murder on the Second Floor by Frank Vosper

Since I brought this up in the thread for Shadows on the Stairs, I figured I'd put in my 2 cents about the play here. I haven't finished reading it yet but it's very good and very exciting. I don't remember much about the movie version to compare the two but I definitely think the play is much better. Bunch of people in a boarding house, the writer in the bunch twisting all the tenants around and turning them into a sinister bunch full of secrets that lead to murder. Very good, if you can find it, I recommend it.