Destroyed by an earthquake and tidal wave centuries ago, the Kingdom of Ekonia fell to the sea floor. Before the survivors could be rescued, they were lost beyond the power of Marcoli's crystal ball to find them. How did the sea swallow them up those many years ago?

The Lost Kingdom introduces Aradia, Archer's guardian and mentor who travels with him through the alien world of the immortals. Can Archer and Aradia find the ancient clues that tell them what happened to the survivors and the purple gemstone trident King Ichos sent to help them? Archer rapidly discovers he needs Aradia's skills to survive the dangers they find at the bottom of the sea.