Written as a sequel to In the Service of the King, Daughters of The Colder Ocean continues the adventures of The Sea King and his magical lineage of The Tuatha De Danann, a powerful and magical race of healers who settled in Ireland, then suddenly and mysteriously disappeared. Torn between two forces; to save the oceans or to save humanity, the Sea King must join forces with either Annika Temple or the queen of the Rusalki. Annika Temple found herself numb with shock after the police showed up at her door to inform her of the plane that crashed into the ocean on its way to Russia, leaving no survivors. Losing her entire family, she found herself alone on the family farm, struggling to function until she found herself pulled into a life of mystery and intrigue, and that she was chosen to help save the entire human race from annihilation. Learning to find her strength and courage, she is confronted by Queen Dannika, queen of the Rusalki, who has devised a plan to stop humans from polluting the oceans. Queen Dannika's plan consisted of annihilating all humans due to seeing many of her Rusalki become terribly ill from the pollution in the oceans, and finding thousands of sharks suffering horrific and painful deaths after their fins were removed. Although, on opposing sides, both Queen Dannika's mission to save the ocean and all sea life, and Annika's mission to save all of humanity needed help from The Sea King and his family of healers, whose underwater kingdom is also threatened with the ravages of pollution.