Meela and Lysi have unleashed Sisiutl, legendary two-headed serpent of the Pacific Northwest. It was supposed to be an ally that would help them win the war. Instead, it has fallen under the control of King Adaro, ruler of the Pacific Ocean. If Meela and Lysi can't stop him, Adaro will use the deadly serpent to rid the oceans of mankind.
With the American military using catastrophic weapons of their own to retaliate, Meela and Lysi must make peace between humans and merpeople before one race destroys the other. The journey will risk their lives and put their relationship to the test-but the vengeance that has been consuming Meela's thoughts, day and night, might prove even more dangerous.