Ambassador of the Nonmalta (E42)

Dan has been warned about a development from a young boy. When Dan gets to the Sea Horse, an underwater city, it spontaneously combusts. The boy, Shinichi, spoke of the Nonmalts being the first rulers of the ocean floor. Anne sees this boy on the ocean floor, put there by early humans. It is not long before Guyros, an octopoid monster of the Nonmalt, appears, alongside a stolen atomic submarine. (Prime Video)