The Ashtown Burials Series (Random House), written by N.D. Wilson, focuses on two siblings Cyrus Smith and Antigone Smith who get involved with a secret society called The Order of Brenden. It is named after the prisons or burials of the transmortals located in Ashtown.
In the first book of the series (The Dragons Tooth), published in 2011, the two swear an oath to an order of explorers who have long served as caretakers of the world's secrets, keepers of powerful relics from lost civilizations, and jailers to unkillable criminals who have terrorized the world for millennia. They search for their missing brother Daniel Smith while trying to earn their places as Journeymen of Ashtown.
In the second book of the series (The Drowned Vault), published in 2012, Cyrus and Antigone have lost the tooth to Dr. Phoenix. The Tooth is the only object in the world capable of killing the long-lived transmortals, and Phoenix has been tracking them down one-by-one, and murdering them. When the surviving transmortals, led by legendary warrior Gilgamesh of Uruk, descend on Ashtown demanding justice, Cyrus and Antigone find themselves on the run in a desperate search to locate Phoenix and regain the Tooth. In the process, they uncover an evil even more dangerous than Phoenix, one that has been waiting for centuries to emerge.