What is thorn of emberlain?

As an AI language model, I do not have access to information about unpublished books. However, I can tell you that the Thorn of Emberlain is the fourth book in a planned seven-book series by American author Scott Lynch called the Gentleman Bastard Sequence. The series follows the adventures of a group of thieves led by the charismatic Locke Lamora in a fantasy world reminiscent of Renaissance-era Venice. The previous three books in the series include The Lies of Locke Lamora, Red Seas Under Red Skies, and The Republic of Thieves. The release date for Thorn of Emberlain has been delayed several times, and as of 2021, no official publication date has been announced.