4 ideas
The fear he spread among individual deputies produced the coalition that brought Robespierre down on 9 Thermidor, while Fouché himself stayed out of sight on the day. Zweig uses the episode to show his method: he did not lead the attack, he made others afraid enough to carry it out.
Fouché's survival rested on switching sides at a precise moment: after a regime's collapse became likely but before it became obvious. Defect too early and you are a traitor to a regime that is still standing. Defect too late and you are one of the losers. Leaving a few days ahead of the majority let him arrive at each new regime as an early ally, already holding claims on it, rather than as a late convert pleading for mercy.
As police minister, Fouché built a network of informers and a store of secret files on everyone who mattered, including his own masters. Because of those files, removing him seemed more dangerous than keeping him, so Napoleon and later Louis XVIII both employed a man they despised and distrusted. Zweig argues that power held through knowledge of other people's secrets outlasts power held through position or loyalty.
Zweig proposes that history is shaped less by the visible, passionate figures than by colourless intermediaries who have no convictions and therefore cannot be broken by events. An impersonal, patient operator like Fouché outlasts the heroes because he has no ideology to betray and no pride to wound. Read this way, political history turns its attention from the protagonists on stage to the operators who survive each change of scene.