David, Christopher, April, and Jalil accomplished what they set out to do in Egypt -- they found Senna's mother and can only hope she provides the Coo-Hatch with a passage back to their own world. But now Neptune, ruler of the sea, is intent on getting the intruders off his ocean -- and down into his world. On the bottom of the sea, David and the others find the lost city of Atlantis. A place where most creatures go, and never, ever return...