Verloc is an Embassy spy in London at the end of the nineteenth century, who is informed by his (rather shady) employers that it is time he earned his pay by doing more than just submitting reports. The choice of action he chooses to appease those at the Embassy forms the basis of the book, and we see how other characters are affected by what he decides.
At times "The Secret Agent" is a little heavy-going - a section near the middle of the book discussing the Assistant Commissioner of Police and a Chief Inspector enlightens us as to these characters but the circular nature of their conversations grates a little and I felt anxious for the action to return to the far more interesting Mr. Verloc & family. Indeed in Verloc, his wife, brother - and mother - in law, Conrad creates entirely credible, very human characters, and their pain is conveyed to the reader in a manner which made me think: "Yes, that's exactly what people are like."
The ending of the book is a little predictable, but skillfully executed. My major criticism would be the depiction of the shadowy revolutionists - I was never quite sure what they were rebelling against, or why, and they were not as credible as the other characters. This, however, may have been Conrad's aim.
On the whole, an original story which is at times very involving. It also has some very funny moments which are usually quite unexpected, but which seem to work, nonetheless.