The novel opens in the ancient Eleusinian wood, where Simon, a cynical soldier of fortune, wanders towards Athens and encounters a young, bookish knight reading the Romance of the Rose. This studious traveler is Rainouart, son and heir of Count Baldwin, Duke of Athens. Rainouart is a man of exceptional physical strength combined with deep spiritual purity, shaped by the memory of his mother, the Lady Isabeau. In the forest, Simon meets Argathona, a dryad whose mother was a true wood-nymph and whose father was a mortal warrior who fell at Troy.
Argathona possesses immortal youth and the ancient wisdom of the gods, who long ago departed for the Hollow Land. Simon attempts to woo her but is easily tossed to the ground by her supernatural strength. Meanwhile, Rainouart is attacked by ruffians in the forest, and Argathona, summoned by her love for the suffering youth, intervenes with a magical storm to rout the bandits.
Tending to his wounds, the dryad and the knight fall deeply in love, discovering a profound connection that transcends their mortal and immortal natures. However, the Duchess Esclaramonde of Thebes—a passionate and manipulative woman who has long desired Rainouart—arrives with a grand escort. Using drugged wine and clever deception, she convinces the disoriented prince that she is his true rescuer and betrothed, leading him away to Athens for a hasty marriage. Simon, who has acted as a spy and observer, follows the events closely until he finds Argathona again.
Despite her grief, the dryad resolves to travel into the human world to save her lover. Disguised as a male knight known as the Prince of Eleusis, Argathona arrives in Athens during a magnificent tournament hosted by Duke Baldwin. Demonstrating incredible prowess, she unhorses the finest knights in the realm, including Rainouart himself, and wins the golden wreath of victory.
Esclaramonde, believing the victor to be a man, invites the stranger to a nocturnal meeting. During the wedding night, Rainouart honors a secret promise made to the disguised dryad: he feigns drinking the poisoned wine prepared by the duchess and pretends to sleep. When Argathona arrives to claim her prize, Rainouart awakens, casts off Esclaramonde's enchantments, and rejects her false advances. In a jealous rage, the duchess stabs Rainouart, but Argathona disarms her and tends to the prince's wound. As chaos erupts in the palace with the Catalan mercenaries and the Theban faction clashing, Argathona mysteriously vanishes into the night. Simon remains behind to guard the recovering prince, while Rainouart is left mourning his lost love, determined to seek her once more in the eternal greenwood.
