First part
The book begins with a prologue which sets up many of the themes that will be explored throughout the work. Zarathustra is introduced as a hermit who has lived ten years on a mountain with his two companions, an eagle and a serpent. One morning – inspired by the sun, which is happy only when it shines upon others – Zarathustra decides to return to the world and share his wisdom. Upon descending the mountain, he encounters a saint living in a forest, who spends his days praising God. Zarathustra marvels that the saint has not yet heard that "God is dead".
Arriving at the nearest town, Zarathustra addresses a crowd which has gathered to watch a tightrope walker. He tells them that mankind's goal must be to create something superior to itself – a new type of human, the Übermensch. All men, he says, must be prepared to will their own destruction in order to bring the Übermensch into being. The crowd greets this speech with scorn and mockery, and meanwhile the tightrope show begins. When the rope-dancer is halfway across, a clown comes up behind him, urging him to get out of the way. The clown then leaps over the rope-dancer, causing the latter to fall to his death. The crowd scatters; Zarathustra takes the corpse of the rope-dancer on his shoulders, carries it into the forest, and lays it in a hollow tree. He decides that from this point on, he will no longer attempt to speak to the masses, but only to a few chosen disciples.
There follows a series of discourses in which Zarathustra overturns many of the precepts of Christian morality. He gathers a group of disciples, but ultimately abandons them, saying that he will not return until they have disowned him.
Second part
Zarathustra retires to his mountain cave, and several years pass by. One night, he dreams that he looks into a mirror and sees the face of a devil instead of his own; he takes this as a sign that his doctrines are being distorted by his enemies, and joyfully descends the mountain to recover his lost disciples.
More discourses follow, which continue to develop the themes of the death of God and the rise of the Übermensch, and also introduce the concept of the will to power. There are hints, however, that Zarathustra is holding something back. A series of dreams and visions prompt him to reveal this secret teaching, but he cannot bring himself to do so. He withdraws from his disciples once more, in order to perfect himself.
Third part
While journeying home, Zarathustra is waylaid by the spirit of gravity, a dwarf-like creature which clings to his back and whispers taunts into his ear. Zarathustra at first becomes despondent, but then takes courage; he challenges the spirit to hear the "abysmal thought" which he has so far refrained from speaking. This is the doctrine of eternal recurrence. Time, says Zarathustra, is infinite, stretching both forward and backward into eternity. This means that everything that happens now must have happened before, and that every moment must continue to repeat itself eternally.
As he speaks, Zarathustra hears a dog howl in terror, and then he sees a new vision – a shepherd choking on a black serpent which has crept into his throat. At Zarathustra's urging, the shepherd bites the serpent's head off and spits it out. In that moment, the shepherd is transformed into a laughing, radiant being, something greater than human.
Zarathustra continues his journey, delivering more discourses inspired by his observations. Arriving at his mountain cave, he remains there for some time, reflecting on his mission. He is disgusted at humanity's pettiness, and despairs at the thought of the eternal recurrence of such an insignificant race. Eventually, however, he discovers his own longing for eternity, and sings a song in celebration of eternal return.
Fourth part
Zarathustra begins to grow old as he remains secluded in his cave. One day, he is visited by a soothsayer, who says that he has come to tempt Zarathustra to his final sin – compassion (mitleiden, which can also be translated as "pity"). A loud cry of distress is heard, and the soothsayer tells Zarathustra that "the higher man" is calling to him. Zarathustra is alarmed, and rushes to the aid of the higher man.
Searching through his domain for the person who uttered the cry for help, Zarathustra encounters a series of characters representative of various aspects of humanity. He engages each of them in conversation, and ends by inviting each one to await his return in his cave. After a day's search, however, he is unable to find the higher man. Returning home, he hears the cry of distress once more, now coming from inside his own cave. He realises that all the people he has spoken to that day are collectively the higher man. Welcoming them to his home, he nevertheless tells them that they are not the men he has been waiting for; they are only the precursors of the Übermensch.
Zarathustra hosts a supper for his guests, which is enlivened by songs and arguments, and ends in the facetious worship of a donkey. The higher men thank Zarathustra for relieving them of their distress and teaching them to be content with life.
The following morning, outside his cave, Zarathustra encounters a lion and a flock of doves, which he interprets as a sign that those whom he calls his children are near. As the higher men emerge from the cave, the lion roars at them, causing them to cry out and flee. Their cry reminds Zarathustra of the soothsayer's prediction that he would be tempted into feeling compassion for the higher man. He declares that this is over, and that from this time forward he will think of nothing but his work.
