An epic undersea adventure from global bestselling author, Rick Riordan. Featuring a brand-new female hero and inspired by Jules Verne's Twenty Thousand Leagues Under the Sea.

Ana Dakkar is a freshman at Harding-Pencroft Academy, training centre for the best marine scientists and underwater explorers in the world. When Ana embarks on the sea trials that mark the end of her freshman year, her life as she knows it is blown out of the water.

She and her school mates witness a terrible tragedy and discover that Harding-Pencroft and their rival school Land Institute have been engaged in a deadly rivalry going back over one hundred and fifty years. With the rivalry turned up full broil, Ana will be tested more than ever before . . .