Royal merman Lir saves human Caleb from a storm and seals a life-blood bond with him, yet Caleb is manipulated by the cruel base boss Kane into believing mermen killed his father. Capturing pregnant Lir, Caleb cruelly cuts off his golden tail and tears out his scales as revenge. After Lir’s twin royal mermaid babies are born, Kane covets their magical power and holds the kids hostage. Gradually, Caleb uncovers the full truth: Kane framed the merman clan and murdered Caleb’s dad himself to steal royal blood power. Bound by the unbreakable blood contract, Caleb and Lir endure endless pain, misunderstandings and separations. They join hands to defeat Kane, sacrifice their lives to save each other, and finally build a peaceful seaside home with their twin children, healing all past wounds together.
