Organized into four books, the long poem Endymion traces the eponymous hero’s quest to gain the heart of the goddess Diana, called Cynthia. Rather than an earthly, corporeal love, however, Endymion’s passion for Diana belongs to the celestial, spiritual realm. He suffers, however, in thinking that he has not risen to this level when he feels the pangs of mortal love for the Indian Maiden. Ultimately, he learns that his heart had been steadfast after all, as the Maiden is Cynthia’s earthly counterpart, and thus he did prove deserving of the goddess.

Endymion’s first book opens with some of the most famous lines that John Keats ever wrote. His attention to the central problem of what constitutes beauty and how to understand it parallels the theme of his “Ode on a Grecian Urn.” Here he celebrates the long-lasting importance of beauty.

A thing of beauty is a joy for ever:
Its loveliness increases; it will never
Pass into nothingness; but still will keep
A bower quiet for us, and a sleep
Full of sweet dreams, and health, and quiet breathing.

The reader sees the young Endymion among his fellow shepherds, who are led by an aged priest, out to pay homage to their god Pan. Endymion is presented as a handsome, smiling paragon. Ganymede was a shepherd abducted by Zeus.

His youth was fully blown,
Shewing like Ganymede to manhood grown;
And, for those simple times, his garments were
A chieftain king’s: beneath his breast, half bare,
Was hung a silver bugle, and between
His nervy knees there lay a boar-spear keen.
A smile was on his countenance . . . .

Those who knew him well, however, could tell that all was not quite right with him, as he was inclined to sigh and pine away. Endymion longs for the love of the glorious Cynthia but begins to despair of being worthy of her. In the second book, he is sent off on a quest into an underworld, where he will prove that he deserves her. He enters the deep, mysterious cavern. As he moves along the path, the lights and forms change before him so he can scarcely find his bearings. The path takes him

Through winding passages, where sameness breeds
Vexing conceptions of some sudden change;
Whether to silver grots, or giant range
Of sapphire columns, or fantastic bridge
Athwart a flood of crystal.

Endymion must endure many travails not only in the cavern but also beneath the sea. By Book IV, he is longing for his native land, thinking he might die, and he wishes he could do so at home. When he finally decides that he is meant to stay with the mortal woman he loves, he tells her of his decision. Miraculously, she is transformed into the goddess’s insubstantial form.

And as she spake, into her face there came
Light, as reflected from a silver flame:
Her long black hair swell’d ampler, in display
Full golden; in her eyes a brighter day
Dawn’d blue and full of love.