After the first chapter, The Living World, which surveys the whole book in one sweep, come nine parts, called shelves, each with a short opening of its own: Animals; Plants and Fungi; Natives of the Planes, the peoples, beasts, and guardians of the Anchors, the Harmonics, and the Veil; Natives of the Zones, the beings that live in the Resonant Zones or that the zones have made; Hosts of the Dark Entities; Constructs; The Risen Dead; Other Beings, those of no other kind; and Touched Beasts, beasts of the world that a zone, a thin place, a ley line, or magic has changed. Within each shelf the entries stand in alphabetical order, one entry to each being. A few titles add a place in parentheses where the plain word would not say whose the beings are, as in Guardians (the Ageless Spring). The sapient peoples of Caeldon are not here: their bodies and lives are told in Foundations.

Each entry opens with a paragraph that says what the being is and why it matters to the peoples. Beside it stands a box headed At a Glance, which gives, where they are known, its kind (fauna, flora, fungus, crop, plane native, zone native, Dark Entity host, construct, risen dead, other, or touched beast), its habitat and range, the peoples it is known to, and its danger: a plain word, harmless, wary, dangerous, or deadly, often with a phrase saying to whom and why. The danger is a description, not a measure for any game.

The sections that follow are always in the same order: Appearance; Habitat and Range; Behaviour and Temperament; Abilities; Life Cycle; Uses and Dangers; and Lore and Belief. Not every being has every section. Abilities are facts of the world, what a being can do and what follows from it, and never game rules. Lore and Belief records what the peoples believe about a being, and belief may be wrong. Knowledge of the planes, the zones, and the Dark Entities is uneven and often mistaken, and an entry says plainly where belief and fact part company, and where nobody knows.

The words the entries use for the planes and powers, Anchor, Harmonic, Resonant Zone, and the rest, are reference terms, not the names the peoples use, which vary by people, faith, and era.

The entries describe each being as it lives in the Medieval Era, around 1,350 CR. Where an entry names a plane, a power, a school of magic, or a people, the place to read more is Foundations: its chapters on the planes, the zones, the powers, and magic explain what so many of these beings belong to. The regions where the animals graze and the crops grow are described in The Medieval Era. A link from one entry to another leads within this book; the website’s Reference at joetjen.github.io/The-Decachord/ has every entry as well, with the rest of the setting around it.

At the back of the book, A Short Chronology gives the nine ages of Caeldon with their spans, for placing what an entry says of a being’s past, and the full chronology is in Foundations. A glossary explains the names and terms the entries use, and an index shows where each is told.

A reference into another book of the series names the chapter or section it points to and adds, in brackets, that book’s short form after the link: (FND). The short forms are: