4 ideas
In July 1945, fire breaks out at the May of Teck Club in Kensington after an old unexploded bomb in the garden detonates. Selina Redwood escapes, then slips back in through the same window while others are still trapped, and returns carrying the shared Schiaparelli dress rather than helping anyone out.
Nicholas Farringdon, an anarchist poet who had romanticized the club as a beautiful, free society, sees Selina save the dress and instinctively makes the sign of the cross. That sight of pure self-regard ends his idealism and starts the conversion that later makes him a missionary martyred in Haiti. The book's claim is that seeing evil clearly can reorient a life as effectively as seeing goodness, because it destroys the flattering picture that was blocking belief.
The narrow window turns thinness, which the girls had treated as a matter of vanity, dieting and hip measurements, into the rule that decides who lives. The building sorts people by body size, not by virtue. That exposes how chance features of an environment, not character, often decide who is saved, while the choices made inside that constraint (Selina's theft, Joanna Childe's staying behind and reciting to calm the others) reveal character.
The narrative repeatedly jumps forward and tells the reader early that Nicholas will die and that the girls' lives will scatter. Knowing the ending moves the reader's attention away from what happens and toward why it matters. Small, trivial acts like trading clothing coupons or borrowing a dress then read as morally loaded, because their consequences are already known.