They Do It With Mirrors recap

Miss Marple visits her old friend Carrie Louise at Stonygates, a family mansion combined with a centre for young offenders. During a dramatic confrontation in which resident Edgar Lawson threatens Carrie Louise's husband Lewis Serrocold, trustee Christian Gulbrandsen is shot elsewhere in the house. The noisy, apparently witnessed quarrel seems to give both men an alibi. Miss Marple treats it as staged misdirection. Lewis and Edgar were collaborators, and Edgar's supposed delusions helped create a controlled spectacle while Christian was killed because he had uncovered Lewis's misuse of trust funds. The conspirators' positions and voices were manipulated like a theatrical illusion. Exposed, both men die in the final confrontation. Carrie Louise remains safe, and Gina and Walter repair their marriage.

Ruth Van Rydock tells Miss Marple that she fears for her sister Carrie Louise, although she can name no specific threat. Miss Marple travels to Stonygates, where Carrie Louise lives with her husband Lewis Serrocold amid a large family household and a residential centre for young offenders. The residents include Carrie Louise's daughter Mildred, granddaughter Gina and Gina's American husband Walter, Stephen Restarick, and the troubled Edgar Lawson. Lewis's reforming mission shapes the entire estate. Edgar's growing claim that Lewis is his father appears to be one of several emotional tensions, while Miss Marple watches the family's resentments and Ruth's unease.

Christian Gulbrandsen, a trustee connected with Carrie Louise's first marriage, arrives unexpectedly and begins a private discussion about a serious concern. That evening Edgar Lawson confronts Lewis in the study, shouting accusations about his parentage and firing a weapon while members of the household gather outside. During the commotion, Christian is found shot in another room. A partly written communication indicates that he had discovered danger or wrongdoing at Stonygates, but its decisive detail is missing. Because the quarrel seemed to keep Lewis and Edgar occupied, the murder appears to require another member of the crowded household.

Inspector Curry examines jealousy around Gina, family money, and the administration of Stonygates. The physical arrangement of the rooms and the witnesses' concentration on Edgar's outburst become increasingly important. Miss Marple doubts that a scene so perfectly timed and dramatically expressed should be accepted as spontaneous. Alex Restarick's knowledge of theatre supplies a useful comparison: an audience can be made certain of events it has only heard or glimpsed. Christian's concern is traced toward financial stewardship rather than a private romance, and the inquiry begins treating the study confrontation as a device that shaped everyone's attention.

Miss Marple exposes Lewis Serrocold and Edgar Lawson as conspirators. Edgar's apparent delusions and armed quarrel with Lewis were staged so that noise, timing, and the household's fixed attention would create false assumptions about where the two men could be. Christian Gulbrandsen had uncovered Lewis's misuse of trust money associated with Stonygates and was killed to prevent disclosure. Once the theatrical construction is understood, the apparent alibi disappears. The final confrontation leaves Lewis and Edgar dead. Carrie Louise survives the shock of Lewis's betrayal, while Gina and Walter reconcile and prepare to build a life away from the tensions that had divided them.

Miss Marple determines that Lewis Serrocold and Edgar Lawson were acting together. Edgar's apparent instability and his armed quarrel with Lewis were a rehearsed diversion that gave the conspirators cover while Christian Gulbrandsen was killed. Christian had discovered Lewis's misuse of trust money connected with Stonygates and intended to expose it. The timing of the supposed siege worked like a stage illusion: witnesses concentrated on the loud scene and accepted the positions it seemed to establish. Once Miss Marple dismantles that performance, the final confrontation leaves Edgar and Lewis dead. Carrie Louise survives the collapse of Lewis's scheme, and Gina and Walter reconcile, leaving Stonygates to continue without the deception at its centre.