Milton invokes a Heavenly Muse to help him describe the “Fall of Man.” The action begins with Satan and his devils in Hell after they have been defeated by God’s army. The devils construct Pandaemonium, a meeting place, and discuss how they will continue their revolt against God. Beelzebub suggests they corrupt God’s new creation, Earth, and Satan agrees. Satan offers to cross the abyss and find Earth alone. As he leaves Hell he meets his children, Sin and Death, who follow him and build a bridge from Hell to Earth.
God predicts that Satan will corrupt humans, and the Son offers to sacrifice himself for humanity’s sake. Satan travels past Chaos and Night and finds Earth. He pretends to be a cherub and sneaks past the angelic guard. Satan enters Paradise and its beauty causes him painful envy, but he resolves to bring evil out of God’s goodness. Satan sees Adam and Eve, the first humans, and overhears them discussing God’s commandment forbidding them from eating the fruit of the Tree of Knowledge.
That night Adam and Eve have innocent sex and fall asleep, and Satan turns into a toad whispering to Eve. The Archangel Gabriel finds Satan and confronts him. Satan considers fighting but then God hangs Golden Scales in the sky and Satan flees. Eve wakes up from a dream about disobedience. To ensure the couple’s free will, God sends the angel Raphael to warn Adam and Eve about Satan.
Raphael eats with Adam and Eve and then describes Satan’s war in Heaven. Satan was jealous of God’s Son, and he convinced a third of the angels to rebel with him. Only one angel, Abdiel, left his cause and returned to God. The angel armies fought, with Michael leading Heaven’s army. The rebels experienced pain but couldn’t be killed. On the second day the rebels fired cannons at the good angels, but then the Son drove them out of Heaven and into Hell. Raphael warns Adam about Satan’s attempts to corrupt him.
Raphael tells the story of creation: the Son created light, then the stars and planets, and then the animals and humans. Adam asks Raphael more about the cosmos, but Raphael warns him about seeking too much knowledge. Adam tells Raphael his first memories and admits his physical attraction to Eve, and then Raphael returns to Heaven.
After seven days Satan returns to Eden and possesses a serpent. Meanwhile Eve suggests that she and Adam work separately. Adam resists this idea but relents. Satan finds Eve and flatters her. She asks how he learned to speak, and Satan says he ate the fruit of the Tree of Knowledge. He suggests that Eve should eat the fruit to prove her courage and to become a goddess, and Eve hesitates but then eats. She offers some to Adam, who realizes Eve has fallen, but he eats the fruit so they won’t be separated. The two experience lust for the first time and have sex.
God sends the Son to punish the couple. The Son punishes the serpent to slither on the ground, Eve to have pain in childbirth and submit to her husband, and Adam to labor for his food. Meanwhile Satan returns to Hell and sends Sin and Death to infect Earth. Satan and the devils are punished by being turned into serpents.
After the Fall, the angels rearrange the earth to make it less hospitable, and the animals become carnivorous and unfriendly. Adam and Eve blame each other and fight, and then Eve accepts the blame and considers suicide. Adam suggests they have revenge on Satan by being obedient to God, and they both weep and repent.
God sends Michael to expel the couple from Paradise. Before he does so Michael shows Adam a vision of the future, including his children’s crimes and many sinful generations, and then the flood, when God kills all humans except Noah’s family. He sees the Tower of Babel, the creation of Israel, the Exodus from Egypt, and finally Jesus as the Son incarnate. Michael explains the Son’s sacrifice to atone for the Fall and save humanity. Adam is comforted, and then he and Eve tearfully leave Eden.