In the book Clockwork Princess Tessa and Jem are engaged. Will still loves Tessa but is torn because of his friendship with Jem. Mortmain plans to use his Infernal Devices against the Shadowhunters.To complete his goal though, he needs Tessa. This was absolutely my favorite book in the whole series. I loved the suspense and how you had to pay attention to the tiny detail. I adore the characters, I think that Jem and Will were both great in their own way. It was a breathtaking conclusion to the Infernal Devices trilogy. I loved how Cassandra Clare describes the characters.