They Do It With Mirrors is a 1952 mystery novel by Agatha Christie.
Miss Jane Marple meets up with her old school friend, Ruth Van Rydock. Ruth tells Jane that she is worried about her sister Carrie Louise, Miss Marple's other school friend. Ruth can't say what's wrong, but she thinks something is wrong, so she wants her inquisitive friend Jane to check it out.
Based on nothing more than that, Miss Marple is off. She goes to visit Carrie Louise, who is Happily Married to her third husband, Lewis Serrocold. Lewis runs a reformatory for teenaged delinquents, a progressive institution seeking to give young criminal offenders the skills to be productive members of society. Jane meets her old friend Carrie Louise, Lewis, and the rest of their complicated household:
- Gina, Carrie Louise's granddaughter. Gina is married to an American, Walter Hudd, but their marriage is in trouble.
- Alex and Stephen Restarick, Carrie Louise's stepsons from her second marriage. Both of them have eyes for beautiful Gina.
- Mildred, Carrie Louise's daughter and Gina's aunt. Resents her mother and her family in general for preferring Mildred's sister and Gina's mom, Pippa, now long dead.
- Juliet Bellever and Edgar Lawson. Juliet is Carrie Louise's longtime secretary and companion. Edgar is one of the young delinquents, a schizophrenic who sometimes thinks he's the son of either Winston Churchill or Field Marshal Montgomery. Despite this handicap Lewis Serrocold is rehabilitating him, and Edgar is working as his assistant.
- Christian Gulbrandsen: Mildred's half-brother and Carrie Louise's stepson from her long-ago first marriage (Carrie Louise was a Trophy Wife and she and Christian are the same age).
Christian, who is a trustee of the reformatory, arrives unexpectedly, and in a state of concern. Soon he is shot and killed! Will Miss Marple discover the murderer?note
- Contrived Coincidence: Lampshaded by Miss Bellever, who says "You don't expect murder and attempted murder in the same house on the same night." Subverted when Miss Marple figures out that it wasn't a coincidence at all, but rather Edgar and Lewis's plot.
- Delinquents: Lewis Serrocold runs a reformatory full of delinquents. Lewis is a crusader aiming to put delinquents back on the straight and narrow.
- Disconnected by Death: A literary variant. When Christian was killed he left behind a letter on a typewriter, that ends with "I have reason to believe that that sweet lady is being poisoned. I first suspected this when—". This is later subverted when it's revealed that Lewis added the bit about poisoning to the end of the letter as part of his scheme.
- Laughing Mad: In the big confrontation where an insane, gun-wielding Edgar is threatening Lewis, Edgar lets out "a laugh that Miss Marple had to admit definitely sounded insane."
- Holding Both Sides of the Conversation: Edgar and Lewis do this to help Lewis establish an alibi. They go into his office, and then Edgar fakes both sides of an argument, loud enough for those outside to hear, while Lewis slips out a back way and commits the crime.
- The Lestrade: Most every Agatha Christie novel had a hopeless detective on hand to make Poirot or Marple look good, and in this case it's one Inspector Curry, who seems to want to arrest Walter for being an irritating American.
- Napoleon Delusion: Edgar Lawson introduces himself to Miss Marple as the son of Winston Churchill and later claims he's the son of Bernard Montgomery. Later subverted when it's revealed that he's faking.
- Never One Murder: Alex Restarick and Ernie the delinquent are both killed near the end of the story. Alex apparently started to figure out how the murder was done, and Ernie pretended that he saw something incriminating. They're both killed when a counterweight is dropped on them at the theater.
- Obfuscating Disability: Edgar Lawson is not really "Edgar Lawson" and he doesn't have schizophrenia. Lewis brought him to the reformatory as part of the murder scheme.
- Penal Colony: It turns out that Lewis Serrocold had a crackpot scheme to found what amounts to a penal colony. He had ambitions to buy an island and set it up as a sort of large reformatory, populated by delinquents. But that would cost a lot of money, which is why Lewis has been embezzling.
- Red Herring: The whole storyline about Carrie Louise being poisoned is misdirection by Lewis, seeking to lure the police away from the true motive. He surreptitously adds a few lines from Christian's letter, invents a story about Christian believing Carrie Louise was being poisoned, and even sends his wife some poisoned chocolates.
- Saw a Woman in Half: Features a lot of discussion of this trick and how it is done. Although no one actually performs the trick during the novel, Miss Marple realizes that the killer's method of murder used a very similar trick.
- Shout-Out: Edgar is said to be having "a state of humility approaching that of Uriah Heep's." This is a bit of foreshadowing as Uriah Heep's humility was fake and so is Edgar's.
- Title Drop: A discussion about how theater is artifice leads to the topic of magicians and how both deceive the audience. Miss Marple says "They do it with mirrors is, I believe, the slang phrase. The talk of actors and magicians deceiving the audience leads to Miss Marple's "Eureka!" Moment.
- Two Dun It: Edgar and Lewis collaborated on the murder, with Edgar Holding Both Sides of the Conversation while Lewis stole off to do the deed.
- The Unfavorite: Mildred, the biological daughter of Miss Marple's friend Carrie Louise, is the unfavorite as compared to Carrie Louise's adopted daughter Pippa, her stepsons Alex and Stephan, and later Pippa's daughter Gina. Poor girl just can't catch a break.
- The end of the story, when Carrie Louise turns to Mildred for support and comfort and an earlier conversation between the former and Miss Marple implies that much of this "unfavoritism" was Mildred's perception.