The Thirteen Months is a book found in Dishonored.
Transcript[]
[Excerpt from a book on the calendar and proper duration of the year]
As was laid down long ago, there are thirteen months, each 28 days in length. In the last hours of the year, the High Overseer will sound the Fugue Feast.

The Thirteen Months.
The Month of Earth
The Month of Seeds
The Month of Nets
The Month of Rain
The Month of Winds
The Month of Darkness
The Month of High Cold
The Month of Ice
The Month of Hearths
The Month of Harvest
The Month of Timber
The Month of Clans
The Month of Songs
Location[]
- The book can be found next to a safe and note on the way to Granny Rags' lair in the Old Dunwall Sewers during the mission, The Flooded District, and only if Slackjaw and she appear at the end of it.
Trivia[]
- The months of Seeds and Harvest were accidentally inverted during the game's development.[1] The official artbook features the correct version of this book.[2]