The eternal ember

In a world where death is a myth, love is the only thing that can kill you.
​The Nine Kingdoms are not ruled by men, but by gods. Immortals who have walked the earth since the first star was breathed into existence. For a thousand years, the Great Treaty of Arkhosian has kept their powers in check. But immortality breeds boredom, and boredom breeds ambition.
​Overlord Ignis, the undying flame of Wyrm-Spire, has played his final hand. He has bound his three sons-Valerion, Kaelen, and Rhogar-to the three rival thrones of the world. In an immortal's life, a marriage is more than a vow; it is a magical tether that merges two ancient souls forever.
​As the princes journey to the crystalline spires of Aetheria, the unmoving castles of Kingsreach, and the shifting tides of Coralis, they discover that their brides are just as dangerous-and as lonely-as they are. But a dark rot is spreading through the Nine Kingdoms. Something is killing the "unkillable."
​From the frozen depths of Jotun-Heim to the silent ruins of Nox-Aeterna, a shadow is rising that feeds on immortal souls. The three brothers must find a way to truly bond with their wives, for only a "Joined Soul" can speak the Arkhosian word that can stop the end of eternity.