The Doctor and his friends find themselves in the lost city of Atlantis, where the crazed Professor Zaroff has convinced the people of Atlantis that he can raise their sunken city from beneath the sea. However, the Doctor discovers a terrible secret behind Zaroff's plan - a secret that could destroy all life on Earth. As the countdown commences to the end of the world, can the Doctor defeat the underwater menace? The original 1967 master recordings of all bar episodes two and three of 'The Underwater Menace' were lost soon after the programme's original transmission. However, audio-only recordings of the missing two episodes have survived and have been used here to create a brand new fully animated presentation of this lost classic.