The Toll (Arc of a Scythe, Book 3) by Neal Shusterman

In the highly anticipated finale to the New York Times bestselling trilogy, dictators, prophets, and tensions rise. In a world that’s conquered death, will humanity finally be torn asunder by the immortal beings it created? Citra and Rowan have disappeared. Endura is gone. It seems like nothing stands between Scythe Goddard and absolute dominion over the world scythedom. With the silence of the Thunderhead and the reverberations of the Great Resonance still shaking the earth to its core, the question remains: Is there anyone left who can stop him? The answer lies in the Tone, the Toll, and the Thunder.