Tales From the Shadowhunter Academy Book by Cassandra Clare

Simon Lewis has been a human and a vampire, and now he is becoming a Shadowhunter. The events of City of Heavenly Fire left him stripped of his memories, and Simon isn’t sure who he is anymore. So when the Shadowhunter Academy reopens, Simon throws himself into this new world of demon-hunting, determined to find himself again. Whomever this new Simon might be.