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As with the first game in the series, the cases you unlock are not completed in the order they appear. In fact, several overlap, with items gained and locations unlocked partway through some cases that are required to complete a case started earlier in the game.

[edit] Prologue

Now, three Gods wait on the windowsill
Where one God's blood was lately spilled

While black tongues lap at the spreading pool
And build the strength they need to rule

—The Quartet for the Dusk of Man