Samejima, Orpheus, and the MIU agents continue their investigation by diving into undersea ruins. But they aren’t alone... Kamuro and his gang are there too, along with some of the baddest and roughest mermen yet! Hope for victory dwindles when Samejima is poisoned in battle and Chako is kidnapped by cult members while in police custody on land. Meanwhile, Kamuro inches ever closer to his prize, the Left Hand of Poseidon.