Ghost of the Shadow Market by Cassandra Clare

This book is a collection of stories developed by not only Cassandra Clare but fellow authors who know how to create a marvelous story line. The book follows a former Shadowhunter,  James "Jem" Carstairs, who is now a Silent Brother known as Brother Zachariah. He is a sworn keeper of the law and lore of the Nephilim of the Shadowhunter world. Of course, as a former Shadowhunter he hasn't forgotten his loved ones when he died in the last story, The Clockwork Princess. The beginning of his journey leads him to the Shadow Market in London where all Downworlders (supernatural creatures) come to buy, sell, or trade magical objects among other things. As the Shadow Market is booming many of the Downworlder's are surprised to see a Silent Brother amidst their stalls. Nevertheless, Brother Zachariah is on  a mission to find out more about Tessa Gray's lineage at her request, and he would never say no to Tessa. Of course, it's later discovered that her lineage is revealed in the book Chain of Gold.  Her son, James Herondale, finds the Greater Demon who helped sire his mother. 

Through the many short stories of the Ghost of  the Shadow Market, Brother Zachariah continues to full-fill a promise he once made to find a missing Herondale. Later this missing Herondale is discovered and saved before harm comes to him, and he makes an appearance in another one of Cassandra Clare's books Lady Midnight. Personally, this compilation is part of a timeline that follows the other stories within the Shadowhunter series and it fills in some of the missing information between the stories, too. If you're an avid Shadowhunter fan then read this book. 

Here's a link that gives additional information of this book Shadowhunter Fandom .