4 ideas
In four-power occupied postwar Vienna, Harry Lime stole military penicillin, diluted it, and sold it on the black market. Children with meningitis who received it died or were left brain-damaged. Lime faked his own death in a street accident, burying an informer in his coffin, until his old school friend Rollo Martins, a writer of pulp Westerns, helped British police officer Colonel Calloway trap him and shot him in the city's sewers.
From the top of the Prater Ferris wheel, Lime asks whether Martins would really feel pity if one of the moving dots below stopped forever, especially if each one paid him thousands of pounds. Physical and social distance strips victims of faces, so harm becomes arithmetic. That abstraction is what makes large-scale, profitable cruelty feel costless to the person causing it.
Martins's childhood hero-worship of Lime survives every legal argument and every accusation from the police. It breaks only when Calloway takes him to the children's hospital ward to see Lime's victims. Loyalty built on personal charm defends itself against abstract charges, and only direct sight of the specific harm forces a person to choose between friend and conscience.
The official story of Lime's death names two men who carried the body. The porter, however, recalls a third man whom no one will identify. A single detail that fails to match a staged account shows that the scene was arranged, and the missing person turns out to be the one who staged it: Lime himself.