Miss Marple is convinced by her old friend Ruth to take a little trip to check on her sister, Carrie Louise. Ruth has a feeling that her sister is in some kind of trouble. When they were girls, they were all pals, but Miss Marple hasn't seen her friend in decades. She is unsure that her visit will uncover anything to reassure Ruth.
Ruth explains Carrie Louise's present circumstances. She's married to a doctor who convinced her to turn her estate into a home for wayward boys. When Miss Marple arrives at Stonygates, she finds chaos. Carrie Louise has a houseful of characters: her daughter, a variety of stepsons, a granddaughter and her soldier husband, Carrie's devoted companion, doctors and their unstable assistant. All these personalities clash but Miss Marple doesn't see anything alarming. Of course, a murder happens anyway after the arrival of another guest.
What I enjoy about Agatha Christie novels is how I never figure out who did the killing until the very end and it always seems so obvious then. Miss Marple also has this experience with magic tricks, once the trick is explained it's so simple. The Art of Magic is in the misdirection. Christie herself was an excellent magician in that sense. Little hints are dropped and you have the feeling that you almost got it when she diverts your attention elsewhere. Tricky, tricky.
Miss Marple is almost fooled. Almost. She's too smart to be tricked for long though. There are a bunch of suspects. The most obvious are ruled out, of course, it's never them, but how could one of the others have done it? None of the suspects realize sweet Miss Marple is as sharp as she is. Inspector Curry sees her for what she is right away and uses her insight to solve the crime, even when some of the things she says makes no sense.
They Do It With Mirrors is one of the most entertaining Christie novels I've read. I enjoyed the trick.