This may be the prototypical Hitchcock Presents episode. It involves an elderly woman who lives in the house of her uncle, a snarly, mean-spirited man who never has a kind word for her. She feeds him, takes care of him, puts up with his crude behavior. She's no prize herself, but she sits and waits, hoping an acceptable person will come along to help her in a murder plot. The one that finally fills the bill is an attractive, middle-aged actress, down on her luck. She has answered a room-for-rent ad and is quickly accepted. As it turns out, she falls into the plot and begins to ingratiate herself with the old guy. Since he never unlocks his door, she is to maneuver herself into his room and then leave his door unlocked. The niece, who seems older than her uncle, will then enter the room while he sleeps and turn on a gas burner and asphyxiate him. Of course, things don't always work out as the plotters wish they would and that's where the twist comes in. A very representative episode. Good character actors and a pretty good prescription.