Modernism; Mystery; Family Drama
The Modernist element of this book is the way that Conrad messes with time. In the first stages of the book, we learn that Verloc needs to initiate an attack on the Greenwich Observatory. Suddenly in the next chapter, we learn that this attack has already taken place, and that someone carrying the bomb has blown himself up.
We are led to think that the person who has blown himself up is Verloc. But wait a second; it turns out that there were two people who got off the train at Greenwich—one husky and one thin. The husky one got away, and we know that "fat pig" Verloc ain't the thin one.
Just as we think the mystery is about to unravel, the novel leaps backward several weeks in time, but as readers, we don't know this right away. Now that we see Verloc and Stevie both safe and sound, we wonder what has happened with the bomb at Greenwich. It's not until Verloc proposes the plan of Stevie going out to stay in the country that we realize the backward leap has happened.
We know that were approaching the day of the bombing after Conrad has already shown it to us, and this strongly contributes to the sense of fatalism and dread that the book conveys. In other words, by showing us the future and then forcing us to move toward it anyway, Conrad makes the events of his book seem unavoidable. More than anything else, his use of time shows us just how little hope there is for people like Stevie in the modern world.
You can go either way on whether you think this novel is a mystery. If it is a mystery, it's not all that tricky. Chances are you were able to figure out who got blown up at Greenwich quite a while before the book reveals it. By having you figure out the mystery before the characters do, Conrad forces you to take part in the inevitability of Winnie and Verloc's destruction.
At its core, this book is also a family drama, since its action results completely from the relationships between Verloc, Winnie, Stevie, and Winnie's mother. Their inability to understand one another leads Verloc to take Stevie for granted and get him killed. His further inability to understand Winnie's love for her brother gets him killed, and finally, Winnie's unwillingness to look beyond the surface of things keeps her from becoming suspicious when Verloc takes her brother out into the country. Oh, yeah: also Winnie stabs Verloc with a carving knife. Ain't no family drama like stabby family drama.