The Elite and the Rogues. The Elite and the Rogues, #6

Alexander Selwood hides many secrets. That he's the first immortal of Cynfor is just one of them. When he decides to help the resistance when his actions lead to putting a friend in danger, he is led down a path that leads him to confront his own past and many dangers, most of them stemming from the immortal despot Thaxter and his bunch of immortal goons called the Elite. Though allied with the Resistance, Alexander's actions often strain the tenuous trust they have in him, with some of his actions and secrets nearly breaking that faith.  The Elite and the Rogues is an omnibus edition containing all five novels as well as the companion piece in The Elite and the Rogues series