The story is part of Clare’s epic bestselling Shadowhunter series and is set in “the Shadow Market” which is a meeting point for faeries, werewolves, warlocks and vampires.”
Here are links to Kobo for the Shadow Market serial so far — the ebooks and audiobooks are available at all the usual ebooksites online:
“Son of the Dawn” by Cassandra Clare and Sarah Rees Brennan
“Cast Long Shadows” by Cassandra Clare and Sarah Rees Brennan
“Every Exquisite Thing” by Cassandra Clare and Maureen Johnson (June 12, 2018)
There will be a total of ten stories, including another story co-written by Kelly Link and Cassandra Clare, which will be published when all ten stories are collected in a hardcover collection in 2019.