The new book will be a crime thriller called The Silkworm. According to reports, the book is slated to hit bookshelves on June 19th. Time has more:
The Silkworm will follow the private investigator Cormoran Strike, who Rowling introduced in Cuckoo, as he investigates the murder of a novelist. The victim penned a manuscript before his death that scathingly mocked a number of public figures, all of whom become suspects.
Rowling released The Casual Vacancy, her first book under the pen name Gailbraith last year. A lawyer at the firm that represents the author leaked the secret, and Rowling sued the firm.