Chapter IV: the Sealed Door
The Barrow Vault opens once you hold the three relics from Chapter II: the coin, the map and the key. Inside, the Guardian waits by The Sealed Door, and there are two ways through:
- Speak the Guardian's whole true name. You learn it in Chapter III: Tamsin at the Standing Stones gives you half, and the rest comes before the chapter ends. A wrong name only fails, and you can try again.
- Fight the Barrow Guardian.
Either way the book goes on. The survey is still unfinished, and that is what sends you north for chapters V to XII.
Chapter XII: the Last Line
At the summit, the survey lies open on the slab. You can end the book two ways:
- Draw the last line and finish the survey. It needs every sheet of the survey in hand: the coast, the cloister, the adit, the northern cairn and the drowned orchard. Each one ends its own chapter, V, VI, VII, IX and X, so you will have them all by now.
- Break the Underlying, by force.
The slab offers other ideas too. They only fail, with a reason, and you can choose again.
Seeing another ending
Either ending finishes the book, opens its free roam and counts towards the fourth book. Free roam has no story in it, so to see the other way you need to read the book again: in another save slot, after a New Game, or with New Game + once you have finished every book.