It depends not on chases and killings, but on devious, greedy connivance in a world where everyone is looking out for himself. His wife works for the director of the Panama Canal company, and in his tailor shop, which doubles as a club where gentlemen can drop in for a drink or a cigar, he overhears a great deal, although not as much as he tells Osnard he overhears. He also has genuine contacts with the hidden side of Panama. Both still hold their political ideals, Mickie loudly and defiantly, which inspires Pendel to invent a fictitious radical political movement, which Osnard believes in for reasons of his own. Secrets create a vacuum that only more secrets can fill, and soon Osnard is making demands on Pendel, whose wife presumably knows the secrets of the canal company - although not the secrets Pendel invents and passes along.
Many thrillers are essentially machines to inject a shock into the audience every few minutes.
And there's room for genuine emotion, too, in the way Harry Pendel desperately holds onto the respectability he has conjured out of thin air.