Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Ironic; Satirical
Conrad would be an awesome snarky best friend and a terrible enemy. Just check out this bone-dry witty passage from Chapter 10:
The Assistant Commissioner, driven rapidly in a hansom from the neighbourhood of Soho in the direction of Westminster, got out at the very centre of the Empire on which the sun never sets. (10.1)
Here, Conrad is slapping England across the face for it's Colonial Empire. The fact that England had colonial outposts all over the world prompted people to say that the "sun never sets on the British Empire." Here, Conrad is being funny and sarcastic; but he's also being really dark. After reading the dreary, foggy descriptions of London throughout this book, it seems more appropriate to say that the sun never rises on the British Empire.
It often sounds as if Conrad is laughing at his characters. The anarchists in this book, for example, are all caricatures of completely useless, do-nothing people. Karl Yundt is a man of "worn-out passion, resembling in its impotent fierceness the excitement of a senile sensualist" (3.7). In other words, Yundt is a gross old man who gets off on thinking about how much he hates the world.
By constantly referring to Michaelis as an "apostle," Conrad also seems to devalue or satirize the supposed grace that this impotent anarchist has achieved. In fact, every character in this book seems to have some flaw or blind spot that completely defines him (or her). When the book does delve into issues of compassion, it never really seems to embody compassion itself, but instead comments from a distance on how truly compassionate people like Stevie or Michaelis will end up getting destroyed by the cruel and corrupt world.