Separation is of course a central theme in this masterful novel, as the characters in this city become forcibly separated from the rest of the world as they stay in quarantine thanks to the plague that gives the novel its title. Note how Rieux tries to describe the feelings experienced by both himself and others thanks to this separation and involuntary exile from the rest of the world:
[T]hat sensation of a void within which never left us, that irrational longing to hark back to the past or else to speed up the march of time, and those keen shafts of memory that stung like fire.
However, Camus uses this theme of separation in order to highlight the way in which the various characters depicted in this town were already separated from each other and from themselves even before the plague. The irony of this story is that freedom and its opposite are shown more to be a matter of personal attitude rather than the result of any imposed limitations such as the quarantine. Camus skillfully shows that the characters in this novel were just as confined before the plague as they were after due to their physical, emotional and psychological separation from each other. Consider what the doctor knows about Cottard, for example:
Meanwhile, however, he informed the doctor that he really knew very little about Cottard, but believed him to have private means in a small way. Cottard was a queer bird. For a long while their relations went no further than wishing each other good-day when they met on the stairs.
Camus therefore presents the main characters as being separated from each other and the rest of humanity even before the plague, forcing his readers to ask themselves hard questions about our understanding and notions of freedom.