Tower (Tower #4)

Only the best of the best remains! Cas and Kimi set off on their own, while Mac is quite impressed by the skills of his new partner, Kylie. But can he trust her any more than he did Cas and Kimi? And Cas comes face to face with the rogue presence who's been disrupting the game. She may not know who he is or what he wants, but Cas isn't going to let his plans get in her way!