Cass (plus her ghost best friend, Jacob) is in Paris, where Cass’s parents are filming their show about the world’s most haunted cities. Sure, it’s fun eating croissants and seeing the Eiffel Tower, but there’s true ghostly danger lurking beneath Paris, in the creepy underground Catacombs. When Cass awakens a frighteningly strong spirit, she must rely on her still-developing skills as a ghost hunter - and turn to friends both old and new to help her unravel a mystery. But time is running out, and the spirit is only growing stronger. 

Regan loves, and is loved, though her school-friend situation has become complicated, of late. When she suddenly finds herself thrust through a doorway that asks her to "Be Sure" before swallowing her whole, Regan must learn to live in a world filled with centaurs, kelpies, and other magical equines - a world that expects its human visitors to step up and be heroes. But after embracing her time with the herd, Regan discovers that not all forms of heroism are equal, and not all quests are as they seem....

The long-imprisoned jinn are on the attack, wreaking bloody havoc in villages and cities alike. But for the Nightbringer, vengeance on his human foes is just the beginning. By his side, Commandant Keris Veturia declares herself empress, and calls for the heads of any and all who defy her rule. At the top of the list? The Blood Shrike and her remaining family. Laia of Serra, now allied with the Blood Shrike, struggles to recover from the loss of the two people most important to her.

Ever since Cass almost drowned (okay, she did drown, but she doesn't like to think about it), she can pull back the Veil that separates the living from the dead...and enter the world of spirits. Her best friend is even a ghost. So things are already pretty strange. But they're about to get much stranger. When Cass's parents start hosting a TV show about the world's most haunted places, the family heads off to Edinburgh, Scotland. Here, graveyards, castles, and secret passageways teem with restless phantoms. And then Cass meets a girl who shares her "gift"....

Laia is a Scholar living under the iron-fisted rule of the Martial Empire. When her brother is arrested for treason, Laia goes undercover as a slave at the empire's greatest military academy in exchange for assistance from rebel Scholars who claim that they will help to save her brother from execution.