A Darker Shore: Letters from Ketterdam (hardcover) Leigh Bardugo

the years since the violent upheaval caused by the auction of Kuwei Yul-Bo, the merchants of Ketterdam have been under attack. Secret businesses exposed. Ships sunk. Slavers hunted as they once hunted their victims. All the work of a mysterious sea captain and her ship, the Wraith.

Now, two investigators meet to uncover the truth behind the latest disaster: a massacre on an island off the shores of Ketterdam. Among the evidence collected is private correspondence between notorious crime boss Kaz Brekker and an anonymous sailor aboard the Wraith known only as “I.”