The Blueprints are papers of plans of a currently unidentified machine (possibly the Nest or The Pendant). It has equations and schematics, as well as mysterious pictures. They appeared at the end of Chained Heat, near Grace Beaumont's computer. Not much is known about them yet, but it might bring the power back. It has something to do with The Blackout. There is also a book with an on/off symbol on the cover.
Related: The Blackout and The Pendant.