Hamilton draws the story of Perseus from the later writers Ovid and Apollodorus, though it was also widely popular among the Greeks. One day, the Oracle at Delphi tells King Acrisius of Argos that the future son of his daughter, Danaë, will kill him. Though Acrisius imprisons Danaë to prevent her from ever getting pregnant, Zeus magically enters the prison. Danaë gives birth to a son, Perseus. Acrisius locks Danaë and Perseus in a chest and casts it to sea.
Danaë and her son eventually wash up at the home of Dictys, a kind fisherman whose brother, Polydectes, is the cruel ruler of the area. Polydectes soon wants to get rid of Perseus and marry Danaë, so he comes up with a plan to kill the young man: he convinces Perseus to go kill Medusa, the horrible Gorgon—an impossible feat for a mortal. The gods favor Perseus, however: he receives a mirrored shield from Athena, a magic sword from Hermes, and information on the location of the nymphs of the North—the only ones who know how to kill the Gorgon—from the Graiae, three supernatural gray sisters with only one eye among them. Perseus craftily steals the eye the Graiae share and refuses to return it until they help him. He eventually reaches the mystical land of the Hyperborean nymphs, who give him winged sandals that allow him to fly, a wallet that expands to hold anything, and a cap that makes its wearer invisible. With these, Hermes' sword, and Athena's mirrored shield—which enables him to avoid looking directly at the Gorgons, which would turns him to stone—he creeps into the Gorgons' cave while they are sleeping. The two gods point out Medusa, the only mortal one. While looking at her in the mirror, Perseus chops off her head and puts it in the magic wallet, then begins to fly home.
Along the way, he comes upon Andromeda, a princess who has been chained to a rock because her mother, Cassiopeia, has offended the gods. A sea serpent is about to eat Andromeda, but Perseus cuts off its head and takes Andromeda as his wife. He returns home to find that Polydectes has driven his mother and Dictys into hiding. Perseus goes to Polydectes' palace where all the evil men of the kingdom are gathered. He marches into the meeting and reveals Medusa's head, turning all the men to stone. He lives happily ever after but only after unwittingly fulfilling the prophecy of the Oracle: while participating in a discus-throwing contest, Perseus accidentally hits and kills a spectator, who is, unbeknownst to him, his grandfather Acrisius.
Hamilton's account of Theseus, the greatest hero of Athens, again draws upon Apollodorus, but it also stitches together details from other writers, some as early as Sophocles. Theseus is the son of the Athenian king, Aegeus, but he grows up with his mother in the south. Aegeus has left a sword and pair of shoes under a giant rock and says that when Theseus gets strong enough to move the rock, he is to be sent to Athens. Theseus reaches maturity, rolls the rock aside, takes the sword and shoes, and sets out on the journey. The dangerous road to Athens is full of bandits, notably Sciron, Sinis, and Procrustes, who delight in torturing passersby. Theseus kills the bandits in the same methods they have used to kill their own victims.
When Theseus arrives in Athens, the evil Medea senselessly convinces Aegeus, who does not realize the stranger is his son, to kill him. At the last minute, Aegeus sees the sword and recognizes the boy. Medea escapes to Asia. Theseus then saves Athens from its obligation to King Minos of Crete. After a son of Minos was killed while a guest in Aegeus's household, Minos beat the Athenians in a war, and now, as punishment, every nine years the Athenians had to send seven girls and seven boys to meet their doom in the Labyrinth of the Minotaur. Theseus offers himself as a victim, promising his father that if he survives, he will replace his ship's black sail with a white one for the return journey so that Aegeus will be able to tell whether his son is alive.
Like Jason, Theseus wins the heart of the enemy king's daughter, Ariadne, who defies Minos and helps Theseus escape the Labyrinth with a ball of golden thread that he unwinds as he walks so that he can find his way back. Theseus finds the Minotaur asleep, beats it to death, and flees to the ship to sail home. Ariadne flees with him, and on the way home, he abandons her when she goes ashore and a fierce wind blows him out to sea. Ariadne dies, which is perhaps what makes Theseus forget to lower the black sail and raise the white one. When Aegeus sees the black sail approaching, he commits suicide by jumping into the sea then named after him—the Aegean.
Theseus becomes king and makes Athens a democracy. He has several minor adventures while king: he helps the Argives after the War of the Seven against Thebes, when the Thebans refuse to allow the defeated to bury their dead (see Part Five, Chapter II); he helps Oedipus and his daughters (same chapter); and prevents Hercules from killing himself after his insanity (see Part Three, Chapter III). Theseus fights the Amazons twice—once attacking them, once defending their attack on Athens—and marries their queen, Hippolyta (also called Antiope), who bears him his son Hippolytus. He is one of the Argonauts (see Part Two, Chapter III) and a participant in the Calydonian Hunt (see Part Three, Chapter IV). He defeats the Centaurs, vicious half-men half-horse beasts, after they kill the bride of his best friend, Pirithoüs. Theseus helps his friend again, when Pirithoüs foolishly decides to pursue Persephone as his next wife. Hades outwits them, tricking them into his Chair of Forgetfulness, which makes their minds blank and paralyzes them. Hercules rescues Theseus, repaying his debt, but Pirithoüs remains there forever.
Theseus's story becomes tragic. He marries Ariadne's sister, Phaedra, who subsequently falls in love with his son, Hippolytus. Hippolytus rejects Phaedra, who kills herself and leaves a suicide note accusing Hippolytus of rape. Theseus curses and exiles Hippolytus, who soon dies. Artemis reveals the truth to Theseus. He then goes to visit his friend, King Lycomedes, who mysteriously kills him.
These two stories reinforce earlier themes about fate and the danger of hubris. When King Acrisius tries to alter fate by locking Danaë up and casting her out to sea, his actions only set the stage for that very fate to be fulfilled. Likewise, when Theseus oddly oversteps his place in trying to help Pirithoüs steal Persephone, he fails for the first time and needs Hercules' rescue. These myths explicate their moral lessons by showing that correct behavior is rewarded but rule-breaking—such as hubris towards the gods—is punished.
As Hamilton points out, Perseus's story almost resembles a fairy-tale, with its magic objects and divine intervention. Hermes and Athena tell Perseus almost precisely what to do. Aside from his wily craftiness with the Graiae, his success is due entirely to his sandals, wallet, cap, and sword. Even his motivation is simple, driven by self-preservation and a desire for a beautiful wife. Once he has won these simple aims, he disappears from our view.
Theseus, on the other hand, has many great achievements, and embodies a more highly developed heroism than Perseus. Right from the start, he seeks challenges and wins by his own hand, lifting the rock his father has placed. Then, in the very act of setting off to find his father, he altruistically chooses to better the path for other travelers by killing the bandits. Theseus promptly volunteers himself as a victim for the Minotaur, out of a sense of kinship with the Athenian youth and a desire to end the unfair tribute in blood. Though Theseus escapes from the Labyrinth with Ariadne's golden thread, he conquers the Minotaur himself. Never one to rest on his laurels, he initiates the institution of democracy, serves as a wise judge in disputes, and comes to the aid of justice when the rulers of Thebes withhold it from the Argives. His constant aim is the impartial and balanced protection of decency and the defenseless, and he faces each new challenge with wisdom, gravity, and bravery.
Theseus's story is enduring and deeply culturally rooted, especially in his native Athens. Perseus's tale, in contrast, is a straightforward adventure of pure good versus pure evil. Theseus's story is more intricate, human, and realistic. Interestingly, few of Theseus's challenges come from pure evil or malice—even the adventure of the Minotaur, which seems a case of simple monstrosity, is more complex and with longer roots. The whole tribute of Athenian flesh to Minos stems from Aegeus's earlier wronging of Minos—the death of a son entrusted to Aegeus's hospitality. Theseus is, then, caught in a complicated situation that predates him. In this sense, his story resembles the great Greek tragedies, which almost universally portray heroes or heroines who begin trapped in the complicated situations they have inherited, and which force them to make difficult decisions through a process of exhaustive soul-searching.