The Age of Fable is a handbook of mythology written for general readers. Its stated object is to teach those who do not yet know the writers of Greece and Rome, or the legends of the Scandinavians, enough of the stories to make the constant allusions in literature intelligible. Bulfinch assumes a reader who keeps meeting the names Jupiter, Pan, or Valhalla in books and wants to understand them.
The opening chapter sets the stage. Bulfinch sketches the Aryan family from which he says the Greeks and Romans descended, explains why the same divinity often carries both a Greek and a Latin name, and describes the Greek picture of the world: a flat disk crossed by the sea, ringed by the river Ocean, with Olympus at its center and happy peoples at its edges. This cosmology becomes the scenery for the tales that follow.
The bulk of the book retells the classical stories in sequence. It moves through the creation and the flood, Prometheus and Pandora, the loves and transformations of Apollo, Bacchus, Venus, and the rest, and the great hero cycles: Perseus, the labors of Hercules, Theseus and the Minotaur, the quest for the Golden Fleece, and the Trojan War with the later journeys of Ulysses and Aeneas. Monsters, nymphs, and oracles fill the gaps between the major figures.
Bulfinch then widens the frame beyond the Mediterranean. Separate chapters take up the modern monsters of medieval lore, Eastern religion through Zoroaster and the Hindu trinity of Brahma, Vishnu, and Siva, and Buddhism. He turns north to the Scandinavian Eddas, Odin and Valhalla, Thor and Loki, and the doom of the gods, then closes with the Druids and the early Christian settlement at Iona.
Throughout, the method is the same. Bulfinch tells each story plainly and then quotes the later poets who drew on it, so the reader sees both the myth and its use. The book is less an argument than a reference shelf: a readable, connected store of the fables that, in his view, a person needs in order to read Western literature with understanding.