Angeles Underground by Sofia Raine

A terrifying commitment. An unexpected enemy. A dark family secret.
After the shocking revelation of what the future holds, Fiona and her archrival, Mallory Fiennes, must commit themselves to Sisters of Mercy Psychiatric Hospital if they wish to continue their journey with the True North Society. It is a very specialized hospital, which caters to a very specific clientele. And if the girls want to get out alive, they must first keep from killing each other.
After Matthew learns that Fiona’s mother is somehow involved with vampires, he’s determined to discover the connection. However, his investigation reveals more questions than answers. Fiona’s mother has a dangerous assassin after her—which also puts Fiona in grave danger—and Matthew must find a way to help her before it’s too late…