Marina, a tailless half-breed mocked by all merfolk, is betrayed on Tide Night by her fiancé Ronan, who chooses her cruel stepsister Zara as his fated mate. Heartbroken, she flees into the forbidden deep sea and is saved by Kael, ruthless Lord of Dark Reef, who leaves an unbreakable bond mark on her neck after one passionate night. Three days later, she is ordered to marry Kael for a political alliance. What she thinks is a cold marriage turns into relentless protection: he defends her, kills assassins, and storms the enemy dungeon to rescue her when kidnapped. When Marina awakens her lost royal gold-tail bloodline and defeats the usurper king, she learns Kael has loved her since the night they met. But their wedding night brings a new, deadlier threat.
