Graham Greene's A Gun for Sale (1936) is not one of Greene's best novels, but it is perhaps one of his most important. It set the stage for what was to come in his ultra-famous novel Brighton Rock, which tells the story of, as the title and some of his previous books suggest, a murder in Brighton. It also, as Penguin Books puts it, provides "a fascinating glimpse into the working mind of a master novelist."
On the other hand, A Gun for Sale tells the story of a vile criminal named Raven (who will be mentioned again in Brighton Rock). During the course of the novel, Raven is told to kill the Minister of War. When he is paid for the assassination, he is given stolen notes. In order to stay alive, he must track down and eliminate the person who double-crossed him and evade the police. In order to do so, Raven must go through a number of startling trials and tribulations.
Upon release, A Gun for Sale was met with solid -- albeit unspectacular -- reviews. It wasn't as popular or as widely-read as some of his more famous books like Brighton Rock or The Heart of the Matter. Still, it was adopted into film and T.V. series a few times: in 1942, in 1957, in 1961, in 1970, and in 1991.