Chain of Thorns is the upcoming third and final installment in The Last Hours trilogy.
The book will take place about a week after the events of Chain of Iron.
Some key word clues Cassie has given on the book are:
Paris, kidnapping, Cornwall, a party where a terrible thing happens, death, inventions, science, secrets revealed, a new Shadowhunter arrives in London.
Cassandra Clare is an American fantasy author. Her real name is Judith Lewis (née Rumelt, born July 27, 1973). She was born to American parents in Teheran, Iran and spent much of her childhood travelling the world with her family. She is a huge fan of fantasy and gothic horror.
She is best known for her bestselling series The Mortal Instruments.