Book 1 is aptly called “The Argument” as it introduces the subject: “man’s first disobedience” (61) against God, which refers to the biblical story in which Eve eats fruit from the forbidden Tree of Knowledge and thus brings suffering into the world. The narrator asks his muse to provide an answer for why Eve and Adam would abandon their Creator. The narrator then shifts the focus of the story to Satan, an angel who conspired to overthrow God and propelled a civil war in Heaven. When God defeats Satan, God expels him and his fellow rebels to Hell.

Satan and his second-in-command Beelzebub consider their deplorable circumstances by a lake of fire. Satan admits that they have lost their battle against God, but he is adamant that all is not lost. Craving independence and freedom, Satan decides to make Hell a new haven for himself and his fellow fallen angels. Although they are disgraced and in a horrifying place, Satan declares, “The mind is its own place, and in itself can make a heaven of hell, a hell of heaven” (73).

Satan pauses to proclaim a lifelong war against God.