When Ruka was younger, she saw a ghost in the water at the aquarium where her dad works. Now she feels drawn toward the aquarium and the two mysterious boys she meets there, Umi and Sora. They were raised by dugongs and hear the same strange calls from the sea as she does.

Jim, Dehdeh and Ruka's mom finally track down Anglade's yacht, but neither the rogue scientist nor Umi or Ruka are on board. All that remains is a cryptic invitation to Jim. While Jim tries to figure out the game his ex-colleague is playing and Kanako dives into memories of her daughter Ruka, the strange seachanges continue around the globe.