There are 2 books in the The Cinder Spires series. The newest book is The Olympian Affair which came out in 2023.

1
The Aeronaut's Windlass

Book cover of The Aeronaut's Windlass
Jim Butcher, the #1 New York Times bestselling author of the Dresden Files and the Codex Alera novels, conjures up a new series set in a fantastic world of noble families, steam-powered technology, and magic-wielding warriors...
 
Since time immemorial, the Spires have sheltered humanity. Within their halls, the ruling aristocratic…
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2
The Olympian Affair

Book cover of The Olympian Affair

The fate of the Cinder Spires may be decided by crossed swords in the next exhilarating fantasy adventure in the New York Times bestselling series of noble families, swordplay, and airships.

For centuries the Cinder Spires have safeguarded humanity, rising far above the deadly surface world. Within their halls, aristocratic…