Arts (Sunday, April 8, 9 p.m. ET)
Here’s a plot that’s supposed to be confusing. That’s the way Agatha Christie makes them, with more twists and turns than an English country lane; it’s just complex enough to make you think and make you watch. This one involves a hidden door, a hidden drawer and a hidden corpse. “I never realized what a terrible lot of explaining one has to do in a murder,” says the star, Penelope Keith.