The following link is to Camus' philosophical work, The Myth of Sisyphus. Part One, The Absurd and Suicide, foreshadows his themes in The Plague.
https://archive.org/stream/CamusMythOfSisyphusAndOtherReadings/Camus%20Myth%20of%20Sisyphus%20and%20other%20readings_djvu.txt